OK! Here's the case:
I believe the first round of interviews begins sometime during December, which means by the time you're taking the DAT schools have already started reviewing applications. Now, as you may know, it takes somewhere between 3-4 weeks for ADA to process you DAT scores and send them out to AADSAS, which means by the time schools have your scores they have most likely chosen the applicants that they want to interview for the first round. So what does all this mean?
Taking the DAT in September will most likely result in a late interview for you, and consider your low science GPA that's not a good thing. Why?
By the time you'll be invited for interview most schools have filled somewhere between 40-60% of their class, depending on how fast their admission process works, which means you'll be competing for fewer open spots, which means your competition will become more intense. Now, considering your low science GPA, your chances may not be very good in such intense competition. However, all of this will change if you end up rocking the DAT. If you come out of that exam with a 22+, not only September wouldn't be too late, but you'll most likely have a chance of getting admission into a decent school. So, at the end it comes down to whether you want to rush your DAT and mess it up or you want to take your time and prepare for it sufficiently, so you'll come out of it with some decent scores?
If I were you, I would choose the second option. Yes, the later you take the exam the less chances you'll have for getting in, but if you end up taking the DAT early and come out with a below average scores your chances will be just as bad!
So, at this time, I suggest you mainly focus on preparing yourself for the DAT instead of worrying about whether or not you're too late!
Good Luck👍