Right now. Yes, right now.
One of the biggest mistakes law students make is putting off practicing multiple choice items and reviewing past essay exams until the very end of the semester. The thought goes something like this:
Multiple choice items and past essay exams are testing my knowledge of the law. I don't yet know or have memorized all of the law. Therefore, I should wait until I do know all of the law or have it memorized.
Now, doing so at the end of the semest may end of giving you a realistic indication of where you are at that point. But it's not the best implementation of these practical skills.
The best way to learn the law is to apply it. And what are you doing when you take multiple choice items and take your professor's past essay exams? You are applying the law. True, you may not have covered a concept yet and so you may get the question wrong. But now you've given yourself a frame of reference and a hypothetical...