I studied sparingly during the last 6 months of my rotation or so, then really focused in the last month after my graduation. Still, in my experience, no adequate amount of time studying ever will help you to know the answers of some impossible questions on NAPLEX. It surely helps if you have some strong clinical rotations where you really learn a lot about the drugs and disease states. The test is designed to test your accumulative knowledge of 4 years in pharmacy school and experience through rotations.