Based upon human stubbornness, every planet will have it's own time and date system that will be divided based on historically obscure details before/during and after colonization. Stuff like Thursday is essentially "Thor's day" and in German it literally says "day of the thunder" (Donnerstag).

ps.: Thursday is also Jupiter's day, so it will probably prevail on any colony / permanent human station orbiting it/it's moons.

pps.: I hope they get over the stupid imperial vs. metric divide though.. that one is really annoying.

Assuming that is anyone left that cares about it.