Research on memory and learning suggests that recall is enhanced by reviewing class material as soon after class as you can. Thus, you may be able to spend 5-10 minutes reviewing class notes right after class, but if you put it off until just before the test, the same recall may require several hours.
From personal experience I would suggest that this works even if it is only mentally. For instance, while going home from class, try to remember a few things that you learned in class (time commitment near zero). I think you will be amazed at how well it works!