I took about six weeks to study before I took it. I studied 4-5 hours each day except the weekends. I'm not a biology or science major, so I really had to hammer the sciences, especially biology (which I still think is the toughest section because of how broad it is).
I would also recommend taking off the day or two right before the DAT, or just very lightly go over everything. It has been proven statistically that people who do that perform better on that type of a test.
AA: 20
TS: 20 (Bio: 18, Gen Chem: 23, O-Chem: 22)