I value sleep very highly, and I'm not a morning person at all. When I have to get up at a certain time, I almost always make sure I'm asleep 8 hours before the alarm clock will sound. I even get in bed about a half hour earlier to give myself time to fall asleep.
I don't usually function very well when I'm sleepy, and I'm not very happy when I have to wake up after having fewer than 8 hours of sleep.