As long as it is before the deadline. I attend a program with a deadline of October 1st, I submitted on September 30th. Like scrawnyguy said, you are only at a disadvantage if the school has rolling admissions or something goes wrong when you submit (happened to me, PTCAS erroneously denied some credits and by the time I finally got them to admit it, I had been denied at a couple of schools). In most other cases, the time of the submission doesn't matter much as long as it is before the deadline. That being said, early is rarely a bad idea.