Here are some tips from people who have created a helpful balance:
I worked part-time off campus all through college. It was tough but manageable because I planned everything out by creating a chart and writing out a schedule for both my classes and my part-time jobs. Since I mostly worked Monday thru Friday evenings and anytime Saturday and Sunday, that left me plenty of time to go to class and get school work done during the day. In addition, I had jobs that weren't too demanding so I was able to get some studying done while I was at work and I had enough time to go to parties after work to make sure I had a social life.
The point I'm trying to make is that the main thing you have to do is plan ahead and write everything out. After you register for classes each semester you'll know your availability to work and if something should change from one semester to the next, you'll have enough time to notify your supervisor.