From what I've heard, the earlier you start the application, the better. If by fall you mean early September, maybe. But I know of some people in my area that got ACCEPTED in the fall; around mid-October. I'm not an expert, a BGO, or anything like that, but the one thing I've heard from every person giving me advice about the application is this: get it done EARLY, get it done AS SOON AS POSSIBLE. The problem with applying so late (assuming you are deemed an official candidate by the prelim app) is that there are so many other things you need to do:
1) Get teacher recommendations
2) Take the CFA
3) Get a medical examination
4) Get all your grades, scores, transcripts assembled
5) Write the personal essays
6) Assemble a resume that highlights your leadership, athletic, and academic capabilities [not sure if a resume is mandatory]
7) Meet your BGO and schedule an interview with her/him
8) Apply for nominations from your Senators, Representative, and VP unless you meet the qualifications for a Presidential nom
9) Fill out the rest of the documentation on the CIS
So, if you can get ALL of that done in a timely manner, then you might be okay with applying in the fall. However, I know that I'll be completing all my paperwork by the summer, and the same goes for all my friends that are applying as well.
Best of luck to you!