Actually, I don't know how much time there is between your last exam and the time you take the boards. I'll try to find that out and see what the deal is. As far as studying, it all depends on how you learn. You'll figure out your study habits when you start dental school. Chances are, they'll be a modification of how you studied in undergrad, which will translate into your board studies. Personally, studying after every semester seems like overkill. You only get 2 weeks off for winter break, use them wisely and have fun. Summer after your first year (before the winter you will take the boards) should give you ample time to have fun and prepare at a moderate pace. Then again, it all depends on the exact date the boards are, if the school gives a week off for studying before them, and how your study habits are.
Don't stress so much about them, yet. They're about 2 years away from you, and you seem more worried than I am. I have a half a year till I take mine. Honestly, summer is going to be my refresher of first year courses (most of whcih are on the boards part I), and as the semester progresses, I will devote much of my free time to keeping up with the new info while maintaining my old info. We'll see how it works, but more info on this about the scheduling of classes and the boards needs to be researched.
BTW, an upperclassman told me he studied the Dental Decks only, and scored fairly well. He easily passed, and that was all he was looking for. So, Tufts definitely backs you up to pass. Getting higher in the 90's, like anything at this level, is progressively harder to accomplish, and will require much more work for each equivalent amount of return. I.E. it costs more work for each point the closer you get to 100.