When do ER interviews start?

My personal experience has been it is more about what needs there are on a team rather than having seasonal hiring.

One of my classmates has already had a few first round interviews, and it appears to be much less structured than banking.

I was referred by a couple employees to one of the senior managers at a large Asset Management firm, and they basically said they'll call me when they need me, but until then to just sit tight. Another major asset manager contact said he would figure out what my timeline might be, and that there was indeed no structured recruiting.

My BB did accelerated interviews in Dec and conducting regular first rounds later this month

I had one BB ER 1st round in November and a superday in early January, another BB had a 1st round in mid-January. From what I gather its not as structured as IBD, but i have a pretty small sample size

ER is all over the place. I already got my SA offer a month ago, as have several friends of mine. We're at a couple different BBs. I recognize that's obviously on the earlier side, though.

Most guys I know are going through their first rounds around now and will likely be flying out in the coming weeks. It's less structured than IBD (to say the least.)