i think the kaplan review book serves as a pretty good brief review of things...it's something good to go through for getting the general picture of things. however there are some big topics (mainly for bio) that require more in-depth studying and you should refer to your textbooks/lecture notes for those. i must say that the kaplan book does a pretty decent job with the ochem portion...just make sure to do as many practice problems as you can (that's what i did and i got a 29 on that section). They don't throw complex reactions at you for ochem...just go back and review your SN1, SN2, E1, E2, aldol condensation, boiling pt trends.
i believe the DAT is valid for one year from your test date...but you should double check with ADA to make sure.