Thanks for another issue!
As for dates and calanders, I like the atmosphere they provide. Unfortunately my players have historically not been interested in those details.
I have taken to using 7 day weeks and 30 day months. This keeps players easily able to relate to time periods but keeps the math fairly easy. If players worry enough about this to see the missing days, I mention a 5 day festival week at the new years. If they really worry about it, I also mention that some years the festival lasts 6 days according to portents from he stars and the predictions of learned sages.
I almost always name these days and months, but my players almost always ignore these details. So I don't usually devote too much time to it. Simple modifications or inspiration from reality usually work best for me(Sun-day, Moon-day, some appropriate god whose name starts with T 's-day, some appropriate god whose name starts with W 's-day, etc...).
For Sci-Fi games I usually either use modern calenders or a "standard" calender (usually involving a more decimal math friendly system). Usually just modern calenders since travel times and the like in rules almost always use these.
-Pyrotech