I chose 9 hrs as my perfect amount. I can function for a few days with much less (say, 4), but when I go to bed at 8:30pm I'll actually wake up all by myself in time to go to work in the morning, hey, even time to eat breakfast!--anything less than 9 and I'm dependant on the alarm (and the snooze button!), have to skip breakfast, and am late to work. Okay, so I actually very very rarely go to bed at 8, so basically, I'm just always late to work. :/