Organic Chem II will be beneficial for the DAT. I would say focus on doing well in your classes and start studying for the DAT 2 weeks after your spring semester in 2018 ends. If you keep on your game and you're organized, you will have no trouble taking the DAT mid to late July and still be right on time in terms of applying. I started studying on June 1st and took the DAT on July 28th and had no problems getting interviews/ acceptances. The main goal is to be organized and have all of your application materials done early (getting references and writing your personal statement/ materials for your committee letter if that's applicable to you). I would start a word document and make a table of your accomplishments/ECs and a brief description of what you did as well as the amount of hours you did for each activity.