This evening I was reading a RPG book where the authors spent seven pages detailing how time passes in their game world. The days and months of the year were given these silly names. The phases of the moon were described, with each given a special name. Worst of all the hours were called out in a quasi-Latin style. It was clear that the intent was to create a sense of verisimilitude for the world that they were describing but instead it all came off a bit contrived and silly. This setting isn't unique in this foolishness. Just a quick pass through my game library and it seems like in practically every amateur and professional setting I've been presented with the latest 'unique' calendar and denotation of time. Over and over again it seems that the authors can't wait to tell me all about how special their world's understanding of time is.
Why, it's not Monday here; it's First-Day.
January? No, no. You're saying it wrong. It's Fireseek.
What time is it? Why it's half past Qui'Tar Jut!
Now maybe you're players are really into learning the minutia of your world and are all about calling the various months by these setting specific names and using the tongue-twisting variations for the hours - but I've yet to play in a group that was willing to expend the effort. Instead the days always revert back to Monday, Tuesday while the hours go back to One O'Clock, Two O'Clock, and so forth.
For a while it bothered me that my players couldn't keep to the imaginary calendars I had brought to them and that they didn't care enough about the days of the week to use their 'proper' names. Then one day I had an epiphany: they don't have time to fool with this stuff because all they want to do is play the damned game. To my players calling Monday, First-Day was useless. It didn't improve their immersion into the game world because it produced a jarring, mental disconnect that pulled them out of it. They had to think to call it First-Day instead of just knowing that it was Monday. Calling January, Fireseek didn't tell them anything useful because they had to remember that Fireseek was a cold, snowy month. All I was accomplishing by forcing such contrivances on them was making my games worse.
As I'm getting older I'm finding that the best policy as a Dungeon Master isn't to get cute and come up with special names for the things I'm doing - after all, my orc isn't any less an orc if I call him a Thute - but rather to build on the cultural and societal touchstones that my players can identify with and readily assimilate into their play. My games use regular names for the hours, days, and months of the year, but major events become the names of the years within the game. When they destroyed the city of Kimber by triggering a massive earthquake that swallowed it whole, the year became known within the game's world as "The Year Kimber was Swallowed." My non-player characters (NPCs) could mention it as a touchstone within a conversation and the players immediately knew when it took place in relation to where they existed in the game now. It gave the world a greater depth than telling them that the year was 447 CY. To them 447 CY might as well be 1779 BC. It was a meaningless number that they weren't all that interested in remembering, but those major events stuck with them and gave them a grounding in the world.