I always adjust, but my minimum to function is 3 hours. During exams periods, I sleep between 4 and 5 hours (or sometimes 3). During normal school weeks, I sleep between 4 and 6 hours.
At those times, the wake up is extremelly hard, but a good shower and I'm ready...to walk to the tram and then fall semi-asleep until I arrive at school (once I totally fell asleep and woke up and had missed my stop).
To compensate, the weekends I sleep...pfou, a lot. Between 10 and 12 hours.
I use to be able to survive a sleepless night but I can't do that anymore. Last time I had a sleepless night, it was at school, because we worked in studio from 6pm to 6am. When I got back home, I immediately fell asleep and woke up at 10pm (and decided "Oh, it's late, so why bother?I'm going to sleep till tomorrow morning").
The truth is, I'm exhausted with my school rythm. But there is a bright side to everything: when I go to bed, I fall asleep impossibly fast and I sleep extremelly well, like a baby.
(And I realized that the more I sleep, the more tired I am because the more I want to sleep even more, know what I mean?)