What an interesting question, @BobbySingler! I'd say I keep pretty standard hours, usually, but a lot depends on what (or how much) I've got on my mind. Quite often I'll go to bed at the regular time and then wake up in the middle of the night for whatever reason, start thinking about a particularly thorny problem, and try to work it through in my head. Next thing you know, I can't get back to sleep and I'm up till the sun. Those are the nights when I just get out of the bed at 3 AM or whatever it is just plug away. No sense tossing and turning all night - I'll only wake up tired having nothing to show for my worrying.

Does that every happen to you?