I was an August test-taker, but I waited to apply. I submitted my AMCAS on June 1 the following year, and it made me one of the earliest applicants instead of one of the latest. I started interviewing at the end of August and finished most of my interviews before Thanksgiving. I got my first acceptance at midnight on Oct. 15, which was about when the August test-takers were just getting their scores back. So, yes, you can apply in the fall after half the interview invites and god only knows how many acceptances have been given out already. But most schools have rolling admissions, and it seems that applying in the fall may put you at a significant disadvantage, especially if you don't have the kind of app that will make you stand out. The only thing more frustrating than spending six months in the "possible interview" pool before finally getting invited in the spring is never getting out of the possible interview pool at all because time ran out before the adcom could get around to inviting you.
Personally, I think a late app is an unnecessary risk to take even if you're a stellar applicant, never mind if you're average. This process sucks so much out of you in terms of time, money, and energy that I'd already made up my mind to get a chemistry post doc rather than go through it all again if I didn't get in the first time. Ironically, that made me especially determined to "get it all right" the first time. 🙂