The key to retaining information is to improve the quality of your study, not the quantity.
Most people can retain maximum focus for no more than an hour (and that is even pushing it). Work in bursts, take short breaks. If you feel overwhelmed and dont want to take a real break, at least shift into a mindless task that will help you later. I will share what I would do everytime my mind started to wander during ochem review.
Flash cards just didn't help me. Take full sheets of printer paper or ruled, it doesn't matter. Title the top of each sheet for one functional group (ie alcohols, aldehydes, ketones, ect.) and write down every possible reaction each group undergoes. That is, write out the starting material, use the reaction arrows (w/ reagents listed), and draw out the final product.
Use the examples from the kaplan book and find others from your old notes. Ask your ochem prof for examples if possible, use old exams, and so forth. This task consumes a good deal of time and requires little to no brain power. It is ideal for doing towards the end of a study session or when your brain is just out of focus. Trying to continue reading chapters and retaining info at this point will only waste your time - but writing out mindless reactions will greatly improve your available study resources for when you feel recharged and ready to retain.
Trust me, once you have solid examples pertaining to every group, you will be able to go through these separate sheets in a few minutes each at rapid and easily repetitive speeds. Before you know it, you will recognize pretty much any functional group/reaction type question that the DAT will throw at you (and expect at least 15/30 questions to be of this nature). The rest of the questions are just memorizing a few rules and unique reactions like diels-alder, grignard, aromaticity, so forth. ochem is less intimidating once you master all of the functional groups. Knowing functional group specifics is also a lot easier than trying to blindly memorize random reactions with no actual order.
This is just one example of how to utilize your time. Obviously if you're just starting to study for the day, don't go about writing down reactions, do it when you your brain is on cruise control.
Utilize as many help resources as you can. Ask upperclassmen pre-dents at your school, take a review course, study with friends, stay motivated.
Obviously what worked for me won't work for everyone, but the key point is not WHAT to study, rather HOW to study. Know your limits, get the most out of your time.
Good luck
