The easiest way I know to make time for exercise is to get it over with in the morning. Not only do you rev up your energy for the rest of the day, but you then don't have to think about exercising again until tomorrow. It's already out of the way, taken care of, end of discussion. If you just can't muster the energy to get out of bed an hour early (depending on when your first class is), set aside an hour in the late afternoon when you know nothing is usually going on (the hour before dinner is good) and get to the gym. Keep in mind that a strenuous exercise session too close to your bedtime can interfere with sleep. You'll have to look at your own schedule and see when exercising works for you.
Exercise does not need to take over your life if you don't let it. Resolve to get some physical activity in each day and then do it. No ifs, ands, or buts. After a while, you won't even have to consider whether or not you have to exercise today. It will become automatic, like brushing your teeth. The key thing here is not to make exercise a burden, or it will silently work itself out of your life.
Find out more about this book:The Dorm Room Diet: The 10-Step Program for Creating a Healthy Lifestyle Plan That Really Works