Completely unchanged timeline from prior years. 6 years ago I received my first invite on 9/1, a few more (maybe 7 or 8) trickled in over the next 4-6 weeks, then the flood after MSPEs are out. Different programs in different specialties review apps and send invites at their own pace. But trust me, almost everybody is starting to look at apps already.
Think about it, if you're a PD at a mid-level university IM program with 40 slots, you need to interview 300-400 folks which means you need to give out 400-600 interviews. And you probably received 2000-5000 applications for those spots. If you wait until Nov 1 to even start reviewing applications you risk not being able to recruit applicants you want because other programs will have already offered them interviews and they may not have enough time/money/interest to come to your program.