text: The most effective study hours are when you are most alert.  For most people, this will be more than an hour after your last meal, not too late in the day or too early.  For me, this is from 9-12 AM, and from 1-4 PM.  If you must study other times, my advice is to change the WAY you study.  The most effective way to study is the way that makes the content interesting to you.  Find something about it that you are interested in, or a reason why you can be motivated to learn it.  Also, if you learn best by reading, read the content.  If you learn best by listening, tape the lecture and listen to it again.