Hi folks! Just wanted to give the perspective of someone who went through this last year:
I applied in mid-June and was complete by mid-July (my college's premed committee thing took a while) almost everywhere. In total, of the 27 schools I applied to, I received 6 interview invites (although to be fair, I withdrew from like 15ish schools as soon as I got in on Oct 15).
The interview invites were spread out as follows: I got 4 in August, 1 in early September, 1 in early October, and 1 in early November. Again, I withdrew from most places except for my highest reaches and/or stuff in cities I wanted to visit by mid-October, but as you see the invites were definitely strangely spread out.
I think it's accurate to think that rolling schools go through the applications more than once, which is why there seems to be a delay for the people who applied early with a lot of the schools. So, say you applied to 20 schools in June/July. Depending on what kind of applicant you are, you might get 5ish interviews in the beginning of those schools' cycles because they really want to meet you and everyone agrees on it. Some schools may decide you're not a good fit for them at all and dismiss you altogether. Other schools may be sort of torn and decide to revisit your file once they see what the whole applicant pool looks like- those are the interviews you'll probably get in October or November or even beyond.
Also, a lot of people end up doing what I did and just withdraw from a bunch of places after the first acceptance, while remaining in the applicant pool only for their top (and often most competitive) choices. Because those tend to be the hardest to get into, though, they're also the ones that are least likely to interview you, which means that if you follow this approach you might not get any interviews at all after that mass withdrawal.
Hope this makes sense!