The Galaxy Express 999 universe is what the Doctor Who universe would look like without the Doctor in it.
Planets exploding left and right, dystopian governments everywhere, evil machine creatures chewing through the galaxies unhindered...Planet Future has only been added to the Galaxy railway system very recently
Not much of wild mass guess truth be told but it rectifies one strange plot hole. The 999 stays on a planet for exactly one local day. They arrive on Planet Future some time during the day but don't leave until the next night meaning the 999 stayed there for sometime longer than one day. A day and a half from the looks of it. The conductor does not act like this is an unscheduled delay and even blows the whistle to warn time is running out. The only reason it might stay longer is if there's some administrative business to attend to (similar to the way the Conductor got two weeks off on one planet) and the most likely administrative reasoning would be ironing out some of the details in the contract with the planet being recently added. Further more the planet is frequently as new, Maetal says it'll look different when they see it next and, most importantly, throughout that episode she seems a lot less certain than usual. She knows much about all the other planets they've been to, likely because she's travelled the line before however it seems likely she has not visited planet Future before.