How can we find out when programs stop sending out invites? When do most programs stop? Is it too early to worry about that?
I received an email from a place today that had earlier offered me an invite. I was holding off on accepting until I figured out my schedule. When they responded to me today they said they have since sent out a second waive and have filled their interview spots. So I am assuming they are done sending out invites, at least until people start cancelling them. Try to understand though that there is significant variation in program timelines, as I know other programs that don't even begin setting out invites until the Deans letter is released.
Bottom line, I wouldn't give up on a place until you have received a rejection letter (or on the more optimistic side have found the place you really want to be and don't want to do any more interviewing).