I stay on as long as possible, usually, but only if there's interesting stuff going on. Right now I can be on almost all day because of Summer vacation, when school starts I'll just be on when I have the time.
Well if Im bored and have nothing to do I can easily kill about an hour or two. If it's late/early depending on how you look at it like 2:00 am on the weekend I'll be here for a few hours.
I go about three or four times between 8:30 and 16:3 (with a break for lunch at 12, to 13)... These are my working hours, so i'm on the computer, totally bored, all the day long...