For chem, all you need is Chad's videos, watch them, take notes, do the quizzes multiple times. Once you think you understand it all, move onto DAT Destroyer. That's what I did, and I had no trouble on the chem section.
Bio: very random, but I think Cliff's AP Bio, Destroyer + physiology from Kaplan should be good. Also, I used datQvault and I thought the scores were pretty reflective of my actual performance, so I would recommend that, but at the very end, I would say around 2 weeks before your DAT.