Many people skimp on sleep because they figure it's not really that important. Your eyes are closed, how much can it matter?
However research shows that doing things while sleepy is like doing them when you're drunk. You wouldn't drive your car when you were drunk! It actually damages your health not to get the right sleep.
In fact you lose time by skimping on sleep. You function so slowly and poorly when you're sleepy (although you of course don't realize it) that you do things far more slowly than if you'd been awake. So if you had just slept that extra half hour or hour you would now be getting far more done.
The book I was reading said, hormone wise, the best time to sleep is between 10pm and 4am (and of course a few hours around that). Of course I'm typing this at 10:01pm so I'm not following my own advice! But I will shortly
