This depends on your degree, university, and year of study. 30 hours/week of class is pretty normal in my program, and I've seen schedules with 40 hours/week. The rule of thumb thrown around is 1 hour in class == 1 hour studying on your own: 60 hours/week. There are definitely design project classes which eat up a disproportionate amount of time on top of that, so that's pretty conservative for some years.

Funnily enough, the time that I have to experiment with side project is during the summer months when I have a full-time job.