I usually stay up to 2.30am on a schoolnight and wake up at 7am. I always regret it, and I'm tired as hell all the time, but come 9pm I start getting energy and I can't sleep until 2.30am. I don't know why, though.
I always go to bed around midnight/1AM. However, thanks to my lovely school schedule I still get 8/9 hours of sleep each night.
A year ago, when I basically was addicted to this website, I stayed up til 3/4AM every schoolday waiting for members from other timezones to get on.
Weekdays: often go around 2am-3am and I usually have to get up at 6am.
Weekends: around the same time but I try to catch up on sleep a little bit so I usually get up 10am-11am.