For program invitation schedules, it is difficult to say. After the MSPE, many programs will be finalizing and by mid-November, I would estimate that most would be live and active.
I would favor for cancellations that they would try to send out invites on a rolling basis. They probably have a waitlist. At the terminal end of the season, I would expect a greater attrition rate as people are tired of interviewing.
As I stated in my previous post, the benefit/harm analysis would favor an e-mail as a beneficial way to show interest. All in all, most programs have probably made decisions, so an e-mail may not make much a difference... but if you get an invite because of the e-mail and showing interest... it will make all the difference.
For the IM match, I believe the initial interview invites will be out by mid-November (still waiting on Harvard, UPenn, NYC programs, and some others). After that, interviews may represent cancellation interviews. I have already canceled 4 interviews before the MSPE, so that freed up some space already.
For the EM match, it is more competitive, and people may hold onto interviews more closely as your ROL may need to be longer to match (I don't have the stats in front of me to see).
Bottom line: Probably not going to hurt e-mailing a program at this point.