There used to be a cool site on the web... I can't find it, maybe it went away. It used to be near top of the first page if you just googled fantasy calendar or something but now I don't see it.
Anyway, it was a neat website that had a script program on it. You could enter in all sorts of parameters like how long the year was, how many months, how many days, names of the months, name of the days, number of moons, how many seasons... and then it would plot the whole thing for you and even tell you the moon phase(s) over the course of the year, when the seasons changed. And it would even through in some cute random events like a comet would be visible this day... meteor shower is visible this week... aura borialis type event this day.
I used that a lot and wish I could find it again.
But now, I basically run time off of the major phases of the day... sort of historical. It's mostly hand-waved from day to day stuff. If the NPC contact tells you to me her at Joe's Pub at mid-day, it is assumed you just do.