It is my understanding, based on talking to people who have already gone through the process, that you can get interviews through December and even into January. This is mostly because people who scheduled too many interviews will start canceling, leaving openings for others. That's why, following advice on this site and auntminnie, if you have not heard from a program that has already sent out some invitations (and that you really want), you should take action NOW. Some people say to email while others say to call. Do whichever is most comfortable for you, or both. Let them know that you would like to be placed on their list for cancelations and assure them that, given the offer, you WILL show up. Put yourself in their shoes and figure out what would persuade you to give one person an interview over another. I say to act now because they have probably already sorted the applications into invitation, reject and hold lists. If you weren't on the first, you at least want to be on the third--and high on that one.