I asked the same thing many years ago and some people replied that the position of the sun in the sky is a better indicator that you should stop playing.

I also second the need to of a clock. Even "Warlock" does not have that and I have to look at the time of the save game after I save to know the time. Very annoying.

I think some clock to add in the game interface is one of the better features added to any game, just because while I like my games to carry me away, I want some visual cue ingame to get my ass into bed, and not forget my surroundings too much
I do tend to get very "tunnel vision"... ish... when I play games that I like.

If someone really wants to use the sun, let them turn it off.

Sincerely
~ Kongdej