If you do have a lot of work to do, use that time to sort your notes or clear up your desk or study with a friend. Your study area should have paper, pens, pencils, erasers, a good dictionary, and perhaps a calculator, ruler, glue, cellophane tape, scissors, etc. With all your material nearby, you will not have to stop to look for something. First, when you are under an imposed time restriction, you use the time more effectively. Second, you learn best in short takes.
Brain waves are like radio waves.
If there is not enough space between inputs, you get interference. The more similar the kinds of learning taking place, the more interference. So separate your study periods for courses with similar subject matter. Follow your hour of German with an hour of chemistry or history, not with Spanish. Do not procrastinate.