Depends on the seeing
I can live on little sleep, used to it after years of young kids and commuting
If the seeing is good I can stay out for hours, or get up at 2am and go to work without going back to bed.. but those nights are rare unfortunately.
When observing on new moon nights, I usually pack it away around 12:30am because I know i'm gonna be woken up at 6am by the kids.
Certainly the stamina isn't the same as it used to be when I was going to night clubs as a 19 year old