Submit the AADSAS application and then take the exam anytime in the next 3-5 weeks. You should still have plenty of time to get a fair shot at the process, especially if your DAT scores are through the roof as many peoples seem to be these days.
If you rock the DAT you'll have schools beating down your door for interviews!
Taking it at the end of September would mean schools get your scores the first couple of weeks of October, and should get you some interviews before the holidays hopefully.
Most importantly, get that application in! That takes MUCH longer to get to the schools than do your DAT scores.
