History Main / SanDimasTime

Not so when San Dimas Time is in effect. Events in two different time periods affect each other a fixed time period apart, with one anchor point being the moment the time traveler left the future, and the other being the moment they arrive in the past. For example, if you go back in time a year and change something, the change will only [[DelayedRippleEffect take effect a year after it takes place]], and vice versa. This means that if you urgently need to fix something in the present and travel 20 years into the past to accomplish it, you do not actually have an extra 20 years before your time runs out. You only have as much time as you would have had from the moment you time-traveled into the past in the first place.

San Dimas Time is related to but distinct from a PortalToThePast, where the time travel mechanism ''itself'' is restrained in what you can do -- you can only travel through time by specific increments, or [[UnstuckInTime you only have a limited period]] before the time travel stops working. MeanwhileInTheFuture and FlashbackBPlot are narrative versions of this; the two eras do not actually affect each other, but we're seeing time pass within them at the same rate.

* In ''Series/SecretsOfSulphurSprings'''s first season, the protagonists find a time-travel portal that takes them exactly 30 years into the past. And in the present, it's just a few days before the thirtieth anniversary of Savannah's disappearance, giving them a deadline if they want to try to save her.

* In the ''Fanfic/PonyPOVSeries'', it's eventually revealed that [[spoiler:Shining Armor's arc, taking place several years in the past, is running simultaneously to the main story, meaning ForegoneConclusion is ''not'' in effect]]. The reason for this is that [[spoiler:Shining Armor literally did not exist until the day Twilight went to Ponyville, having been inserted into the timeline to be the [[ForWantOfANail nail between the main world]] and [[BadFuture Dark World]], and thus he's experiencing time differently]]. This continues until [[spoiler:his place in the timeline is cemented, causing the present to wait for him to "catch up" before moving forward]].

* ''Anime/TimePaladinSakura'' seems to run on San Dimas Time; for instance, Sakura hears that her base is being wrecked in the past and only sees it wrecked after that happens.

** ''Film/BackToTheFuture1'': Marty laments that he'll be too late to warn Doc of his fate once he gets back to 1985 -- until he realizes that he has a time machine, and he has all the time in the world. Unfortunately, he doesn't think to give himself any more than just ten minutes, and the [=DeLorean's=] engine is [[MyCarHatesMe not obliging]], so he ''still'' doesn't make it in time to save Doc. [[spoiler:Fortunately, Doc decided to [[TrickedOutTime bend the laws of history]] and read Marty's letter from 1955 anyway.]]

Not so when San Dimas Time is in effect. Events in two different time periods affect each other a fixed time period apart — for example, if you go back in time a year and change something, the change will only [[DelayedRippleEffect take effect a year after it takes place]], and vice versa. This means that if you urgently need to fix something in the present and travel 20 years into the past to accomplish it, you do not actually have an extra 20 years before your time runs out. You only have as much time as you would have had from the moment you time-traveled into the past in the first place.

* The short story ''[[http://www.tor.com/stories/2011/08/wikihistory "Wikihistory"]]'' by Desmond Warzel would seem to operate on San Dimas time; otherwise there would be no suspense regarding [=AsianAvenger's=] return.

* The high concept of ''VideoGame/SpiderManEdgeOfTime'': Actions in the present alter the future, but they do so "simultaneously" in relation to the PortalToThePast; if Franchise/SpiderMan can't stop the giant robot from ever being built "before" it kills ComicBook/SpiderMan2099, then it's too late. Miguel {{handwave}}s this as a side effect of the permanent connection between the two time periods; Peter {{lampshade|Hanging}}s that it still doesn't make any sense.

** In the first ''Film/BackToTheFuture1'', Marty laments that he'll be too late to warn Doc of his fate once he gets back to 1985 -- until he realizes that he has a time machine, and he has all the time in the world. Unfortunately, he doesn't think to give himself any more than just ten minutes, and the [=DeLorean's=] engine is [[MyCarHatesMe not obliging]], so he ''still'' doesn't make it in time to save Doc. [[spoiler:Fortunately, Doc decided to [[TrickedOutTime bend the laws of history]] and read Marty's letter from 1955 anyway.]]
** In ''Film/BackToTheFuturePartII'', Doc rushes to get Marty in position to pretend to be his own son in 2015, and his watch is synced up to 2015 time to make sure he's got his timing right. But if he's wrong, he's got a time machine and can start again- except he doesn't seem to realize this as an option.
** Much of the tension comes from direct causality; in Part II they recognize that the 2015 Biff changed the distant past to create an AlternateTimeline when they returned to 1985. Marty initially suggests going back to 2015 to stop Biff from changing the past, but Doc points out the alternate timeline will have reached 2015, so they need to figure out when in the past Biff changed the timeline.
** In fact, this leads to this issue: since they learned that Biff won his first millions at the horse race on his 21st birthday in 1958, which was in one of the books that Doc brought from the library, and after Marty learned about the earliest point being 1955, Marty and Doc never seem to think of going between then and 1955 to steal the alamanac back at a better point in that three year span of time so that they wouldn't risk running into Part I Marty and 1955 Doc.

** In the first ''Film/BackToTheFuture'', Marty laments that he'll be too late to warn Doc of his fate once he gets back to 1985 -- until he realizes that he has a time machine, and he has all the time in the world. Unfortunately, he doesn't think to give himself any more than just ten minutes, and the [=DeLorean's=] engine is [[MyCarHatesMe not obliging]], so he ''still'' doesn't make it in time to save Doc. [[spoiler:Fortunately, Doc decided to [[TrickedOutTime bend the laws of history]] and read Marty's letter from 1955 anyway.]]

* Because of how time travel works in ''Manga/TokyoRevengers'', Takemichi has to time travel to the exact date something happens and fix it on that day or else he can never go back to that date again. Additionally, for every second he spends in the past, the same amount of time passes in the present.

** Subverted in a 1990s ''Superboy'' story, when the Legion lose a member in the timestream. The Legionnaires insist they need to find her as soon as possible, before something happens to her, to which [[Characters/LegionOfSuperHeroesSilverAge Brainiac 5]] replies, "Doesn't anyone realize we're talking about time travel?"

** In fact, this leads to this issue: since they learned that Biff won his first millions at the horse race on his 21st birthday in 1958, which was in one of the books that Doc brought from the library, and after Marty learned about the earliest point being 1955, Marty and Doc never seem to think of going between then and 1955 to steal the alamanac back at a better point in that three year span of time so that they wouldn't risk running into Part I Marty and 1955 Doc. Even Jeremy Scott of ''WebVideo/CinemaSins'' points this out in his ''Everything Wrong With'' video on the film.
--->"There's no reason why Doc and Marty needed to risk anything tonight. It took 3 years for Biff to win his millions at the horse race. So why not wait until a much better time to the almanac back?"

* In Creator/HarryTurtledove's ''Literature/TheGunsOfTheSouth'', the time machine used by the Afrikaaners to alter UsefulNotes/TheAmericanCivilWar only works in increments of exactly 150 years. This is why they had to rush to steal it in 2014 (any later and no amount of intervention would have changed the outcome), as well as the reason why they show up in the relatively quiet Winter of 1864, rather than at a more critical juncture like the Battle of Gettysburg.

** Basically ignored in the ''Series/StarTrekVoyager'' episode "[[Recap/StarTrekVoyagerS5E6Timeless Timeless]]", where the ship was destroyed in an attempt to return to Earth using an experimental new drive system leaving only Chakotay and Harry Kim as survivors. Fifteen years later, they find ''Voyager'' and retrieve the holographic Doctor, hoping to use Seven of Nine's Borg components and salvaged Borg technology to transmit equations into Seven's Borg implants moments before her death so that the propulsion system won't suffer the errors that caused ''Voyager'' to crash. When the initial transmission fails, the Doctor points out that they can easily call ''Voyager'' again as "the past isn't going anywhere", but that doesn't help if Harry doesn't know what revised equations to send the past crew. Ultimately he has to abandon the goal of getting ''Voyager'' home in favour of aborting the slipstream flight before ''Voyager'' crashes.

* ''VideoGame/SonicTheHedgehog'':

In stories involving time travel, sometimes characters are faced with a time-sensitive problem that can only be fixed by traveling into the past. For example, something bad is going to happen in ten days, so the heroes travel 20 years into the past to prevent it. Except now they're in the past, and from their perspective the event they are trying to prevent is not days but ''decades'' into the future. They should have ten days ''plus'' 20 years to prevent it, right?

** Basically ignored in the ''Series/StarTrekVoyager'' episode "[[Recap/StarTrekVoyagerS5E6Timeless Timeless]]", where the ship was destroyed in an attempt to return to Earth using an experimental new drive system leaving only Chakotay and Harry Kim as survivors. Fifteen years later, they find ''Voyager'' and retrieve the holographic Doctor, hoping to use Seven of Nine's Borg components and salvaged Borg technology to transmit equations into Seven's Borg implants moments before her death so that the propulsion system won't suffer the errors that caused ''Voyager'' to crash. When the initial transmission fails, the Doctor points out that they can easily call ''Voyager'' again as "the past isn't going anywhere", but that doesn't help if Harry doesn't know what to tell the past crew.

** ''VideoGame/SonicTheHedgehog2006'' involves, among many other confusing things, the main trio getting sent to a BadFuture, where they discover that Elise died when Eggman's battleship exploded the day after they left. Tails says, "If we don't return in time, Elise will die on board Eggman's battleship!" [[spoiler:Sonic actually ends up being too late to save her anyway -- which he fixes by simply hopping back in time a few minutes]].

** ZigZaggingTrope in the ''Series/StarTrekEnterprise'' episode "Future Tense". The crew encounters a time traveler from the future and activates his "homing beacon", so his people from the future can find him. Once it's activated, he and all his devices are instantly transported back home. Captain Archer notes that once they got the beacon's signal, the future people could take all the time they need to retrieve him. Except if the beacon is activated in the past, the future people should see it at any time -- even [[MindScrew before the ship travels back in time to begin with]].
** Averted in the ''Series/StarTrekDeepSpaceNine'' episode "Time's Orphan", when eight-year-old Molly O'Brien falls into a PortalToThePast, which closes after her. Though the crew has to spend a few hours reactivating it, according to Odo, the plan is to beam Molly out "a few minutes after she fell". It's then averted in the other direction, when a problem in the transport results in them beaming Molly out ''ten years'' after she fell. It's also mentioned that it might be possible to try again and potentially beam Molly out at an earlier point in time, and the only reason they don't is because it would erase the older Molly from existence and they're not comfortable with that. Continues at the end of the episode; [[spoiler:when the older Molly reenters the portal, she arrives on the same day that she initially fell through, and when her younger self is returned to her own time after all, from her perspective she's been gone for less than a day, even though it's been at least several days for her parents]].
** In ''Series/StarTrekDeepSpaceNine'' episode "Past Tense", Sisko and Bashir accidentally interfere with a riot that was supposed to lead to the social change that helped the creation of the Federation. Cut to characters who are still in the series' normal future time period, who see the Federation disappear at that moment despite the critical event happening centuries ago! The same happens in reverse when they put things right... [[{{Fanon}} Perhaps]] the [[{{Technobabble}} microscopic singularity that interacted with the chroniton particles to produce a temporal energy surge]] acted as a tiny time portal to keep changes in both timelines "in sync" until the situation in the past was resolved.

->''"The clock in [[TropeNamers San Dimas]] is always running."''

** Subverted in a 1990s ''Superboy'' story, when the Legion lose a member in the timestream. The Legionnaires insist they need to find her as soon as possible, before something happens to her, to which ComicBook/{{Brainiac}} 5 replies, "Doesn't anyone realize we're talking about time travel?"

** ''ComicBook/TheCondemnedLegionnaires'': Since they need ComicBook/{{Supergirl}}'s help, the Legion wonders whether she will be available to travel to the 30th century...even though they can choose when she will receive their distress call, and Kara can take as much time as she wants before departing and still arrive in time. When Supergirl makes it to the future, a narration box notes she has taken an incredibly short time, even though she logically should arrive as soon as the call was sent.

* In ''ComicBook/DaysOfFuturePast'', ComicBook/KittyPryde is psychically sent back in time to her younger body before the BadFuture happens. While she's in the past trying to prevent the assassination that would cause the BadFuture, her friends lug her unconscious body around trying to keep it safe from Sentinel attacks. They don't know for sure if San Dimas Time is in effect, but they don't want to take the chance. They wonder if their timeline will be erased when Kitty completes her mission. In the end it isn't, creating an AlternateTimeline.
* ''ComicBook/ScoobyDooTeamUp'': In "Scooby-Doo, When Are You?", a scientist from ''[[WesternAnimation/TheFlintstones the Flintstones' ]]'' time tests a TimeMachine by pulling Mystery, Inc. from the "future" and tells them it'll likely take from three to four years before he's able to send them back. Shaggy is worried because he forgot to water his plants. The Great Gazoo tries to use his power to send them back but he "overshoots" and sends them to ''WesternAnimation/TheJetsons''' future ("Recap/ScoobyDooTeamUpFutureShocked Future Shocked]]"). An archaeological team working for Mr. Spacely had already found the time machine by then and George Jetson uses it to send them to the very point in time [[AvertedTrope it took them from in the first place]].

* Called out and then explicitly averted in Larry Maddock' "The Flying Saucer Gambit", #1 of of the "Agent of T.E.R.R.A." series. The main character has a ''Main/TimeMachine'' and is employed as an agent of the [[Main/FunWithAcronyms Temporal Entropy Restructure and Repair Agency]], with a [[Main/SetRightWhatOnceWentWrong License to Tamper]]. [[Main/ChekhovsGun The system won't let him go back to any point in time that he already exists in]]. At one point he is in the middle of a battle when he uses the time machine to jump 20 years ahead, and the first thing he does is take a nap. He [[Main/MrExposition then reflects]] on how he can jump back to re-join the battle milli-seconds after he left, and not one person will be injured or killed even if takes years to plan out what he needs to do to help his side win the battle.

* Played with in "Literature/TheDandelionGirl". Time machines are set to travel a certain distance, meaning that if one was set to travel to July 7th 1950 today, it will travel to July 8th 1950 tomorrow unless you change the settings, and Julie simply chooses not to do that [[spoiler:until the final journey, where she programs it to travel a couple of decades further.]]

** Averted in the ''Series/StarTrekDeepSpaceNine'' episode "Time's Orphan", when eight-year-old Molly O'Brien falls into a PortalToThePast, which closes after her. Though the crew has to spend a few hours reactivating it, according to Odo, the plan is to beam Molly out "a few minutes after she fell". It's then averted in the other direction, when a problem in the transport results in them beaming Molly out ''ten years'' after she fell. It's also mentioned that it might be possible to try again and potentially beam Molly out at an earlier point in time, and the only reason they don't is because it would erase the older Molly from existence and they're not comfortable with that. Continues at the end of the episode; [[spoiler:when the older Molly reenters the portal, she arrives on the same day that she initially fell through, and when her younger self is returned to her own time after all, from her perspective she's been gone for less than a day, even though it's been at least several days for her parents.]]

* In the first season of ''Series/Dark2017'' we are introduced to two working time machines--a 3-way tunnel in the caves, and a portable machine kept in a suitcase--which are both limited to trips in increments of precisely 33 years. So if a character travels from 2019 to 1986, spends a day in 1986 and then returns to 2019, they will find that a day has passed in 2019 as well.

How or why time travel works like this is rarely answered, [[VoodooShark at least satisfactorily]]. If it is addressed, it's often blamed on the TimeyWimeyBall, the need to avoid {{Temporal Paradox}}es, or just preventing the obvious questions when you complete your journey, arrive at the same time you've left, but appear to have aged several years. It's also useful when you're communicating live with someone in a different time period (like some sort of inter-temporal telephone), to ensure no bizarre relativistic effects. However from a simply [[WatsonianVersusDoylist Doylist]] point of view, giving yourself more time via time travel would be a violation of the RuleOfDrama; the plot needs ''some'' tension to keep the plot interesting.

In stories involving time travel, sometimes characters are faced with a time-sensitive problem that can only be fixed by traveling into the past. For example, something bad is going to happen in ten days, so the heroes travel 20 years into the past to prevent it. Except now they're in the past, and from their perspective the event they are trying to prevent is not days but ''decades'' into the future. They should have 10 days ''plus'' 20 years to prevent it, right?