It depends. Lately, I try to sleep more.
For instance, my team was working on a design project for my microcomputer design clasee (500 level) until 12:30 or so. I got to sleep around 1, up at 7. 6 hours is less than my minimum. I finally got my body adjusted to 7 hours a night, and when i get less, it sucks.
I used to go to bed around 1-2, up at 6:30 on weekdays, with 10 hours or more on hte weekend. I did that for about a year, then realized it was really, really bad for me. Now, i try to get at least 7, the reommended minimum. I really fell a lot better now that I get more sleep.