I always sleep exactly 8 hours every night - regardless of the time I go to bed.. The only time that varies is if I wake up because I'm sick - or if I've been having nightmares..
There have been times when I really, really wished that I could sleep "late" - meaning 10 hours, rather than 8 - or even 9 hours instead of 8 - but I just can't do it.. Once I wake up, I feel like I'm wasting precious time if I don't hop right out of bed and get moving..