I submitted my secondaries beginning 8/21, with the last one submitted on 9/4. I've heard back from 4 schools so far, still quite a few to hear back from.
Anywhere from late august to late november. Applications are not neccesarily prioritized, evaluated, or reviewed in chronological order. superstars, URM, SES, alumni, linked programs, associated undegraduate schools, and other factor can push applicants forward or back in the queue