Every week. Test week shouldn't need to be a huge ramp up, because you are reviewing all along, except you work that whole weekend, not half, during those weeks. Basically every day you read the next days lecture notes and syllabus, review the current days lecture notes and syllabus, and attend lecture. On the weekends you review and organize the weeks material (weekends are key, because they are the only day you aren't getting new material, and so you can iron out your knowledge on things, incorporate outside references, etc and then you glance over everything the week before the test as well. This basically gives you four passes through the material, which should be enough for most people. They key is to cement knowledge into your head, because you will need as much of it as possible in your longterm memory for Step 1 and the wards. Cramming the week before simply doesn't accomplish this as well. So a decent amount of daily review is critical. It's not like college, where once you pass the test you are done with the material. You guys have to shake that mindset. Arguably the grade on the med school test itself is a lot less important than "knowing" the material a year later.
At many med schools, if you spend only 1 hour a day, you either better be an unbelievable genius (there's always one, usually not as many as people think they are) or you are likely to be repeating things. It's hard to fail out of med school, but failing a test is remarkably easy some places if you don't put in the time each week. And the tried and true method for med school is multiple passes through t he material, on a consistent basis. For most of us, there are no good short cuts. If you dont attend lecture, that's fine, but lecture counts as a pass through the material, so you ought to be replacing it with something. Where I went to med school, lots of people tried the skipping lecture method. Those that replaced it with book learning covering the same number of passes through the material did great. Those that used that time to procrastinate and goof off, and really needed lecture to force them out if bed each morning did not.