I wouldn't worry about DAT for now. Focus on getting as of a GPA as you possibly can, especially in those science prereqs! Make sure you don't cram for biology, try to learn it so it sticks. If you do well in your sciences, you'll have easier time reviewing for DAT. Aaaand you'll have a killer GPA which will be amazing! I took ~4 month to prepare for the test, but I never studied for more than 7 hrs/day (usually ~4hrs/day) and rarely studied on weekends. If you can afford such luxury of having a free summer with minimum of other obligations, that would be my best recommendation!