You could start hearing around mid October, but that would be on the early side. It is definitely different for Peds (Primary Care) versus Ortho (Surgery). In Ortho they want to have all their apps in and then send out invites because they are limited how many they interview and they always have specific interview dates to offer. That is not always the case for other specialities. I know someone going into Family. They heard from almost every program they applied to within two weeks and they actually turned down one of the interviews- why because they weren't as interested in the program and they only offered a few interview dates and you had to interview in groups, versus most interview offers they got the date was flexible and it would be in small groups.
So to answer your question- do not worry, it is definitely different for Peds versus Ortho. Going along with that, expect to pay for every part of the interview process (hotel, flight, gas) except for the interview meals. However for some peds programs they will not only provide meals but also pay for the hotel.