Absolutely. Sleep is the key.
There's no point learning anything if you're too tired to get it out of your head when it counts. Try to keep your body clock in order.
The worst thing you can do is be sitting in an exam when your body is in the rhythm of think it should be asleep at that time.
I don't know about you guys but my brain works like bollocks if I am usually asleep at that time and had to get up early.
I've found life much easier since I've been forcing myself to be in bed by midnight at the latest this semester. It was the biggest workload I've ever had combined with the number of hours I am doing at work. 7 days a week of either work or uni or both.... I just couldn't keep doing the late nights of study/procrastination/stuffing about.
You're better off hitting the books until it's time to get to bed... get as close to 8 hours sleep as you can, get up, do some exercise, grab a hot shower and eat a good, healthy breakfast.... then hit the books hard. I'm in the middle of my mid-year holiday at the moment and I've just started exercising again... I was really slack last semester.... no exercise... ate nothing but rubbish. Not good. I'm going to have to do better next semester.
Only productive hours of study count. I've found that out the hard way.... I ended up with a real mountain of work to do at the last minute last semester. I stuff around too much at home, so I'm going to have to lock myself away in the library with some ambient music on the ipod.
4 hours of work in that setting was equal to at least 2 days of work at home for me. I'm shocking.
A guy whom I worked for about 5 years ago had the attitude to uni/college nailed. "Treat school as a 9-5 job..." "It doesn't matter if you've only got one class that day, there is always something you could be doing." If you've got the dedication to do it and your working commitments allow, he's dead right. The only way to guarantee top grades is to put in the hard hours.