Couple ideas I came up with:
The ability to eyeball the time of day An unlock-able recipe for a pocket-watch or wristwatch
Approximate time would be like: Dawn, Morning, Noon, Afternoon, Dusk, Twilight, Midnight, Oh-dark-thirty.
And you wouldn't be able to approximate the time if you couldn't see the sun.
The watch would be an item that, once acquired, allowed you to have a more accurate time.
It could possibly require you to set it once at noon before you could use it.
But it's just ideas, no clue how hard it would be to implement or whether it'd be a good fit for the mod.