every school is different. from what i've gathered, state schools tend to favor applications that come in as early as possible. private schools like usc, bu, and tufts don't usually don't start until about now or in the next couple of weeks. then again, you have schools like nyu who have started sending out invitations.
best piece of advice: look on the schools' websites, and/or call them up and ask for yourself. they're usually really nice about it