If your cGPA is around a 3.4-3.5 by then, and your MCAT is atleast a 26-27, then yes its 50/50, but you failed to mention if these are repeats or first time pre-reqs?
But eitherway, I cant imagine a couple of classes during the summer can raise your GPA by that much, what pre reqs are they, remember you also have to study for the MCAT....
Honestly I cant disagree with the previous poster, that if your bordering on your cGPA and sGPA, you may just want to take a gap year....I am applying in the same cycle, and to be competitive you need atleast a cGPA of 3.4, sGPA 3.2, only then does an MCAT help you get through if your GPAs are flirting around those numbers, a subpar GPA cant be overcome by an avg. MCAT based on my understanding.....
As far as time is concerned, you can apply early, have all your stuff in, to get the ball rolling, but without an MCAT theyre not going to loot at your application. Anything before August is early, August to September/October is normal......and anything after that is getting late...
Ive read for every month you are late after August, start add one point to your MCAT total (i.e. 26 avg, 27=September, 28=October...etc), just to give you a gauge....because people applying late are usually taking their MCAT late or repeating the MCAT to get a higher score....