It depends (at least that is my case). Got my secondaries in for 6 schools back in July/August, heard back from 3 of them within a month (2 interviews and 1 interview waitlist). As for the other 3, its December and I still haven't heard from them (PCOM, NYCOM, NSUCOM).
Moral of the story: don't hold your breath, unless you've got a killer app. Call them if you haven't heard within a month and ask what the deal is. And be sure to verify your app is complete. Good luck!