I did my interview on 1/19 and received the admission letter on 2/4, so about two weeks. I was surprised it came so early. Good luck with your interview!
I got an invite from UNC BBSP in early December. The deadline for interview acceptance was Dec 11 so I'm guessing they're done sending out invitations by now. Sorry for the bad news
I heard back from Vanderbilt and UNC. I applied before the priority deadline so maybe that's why I received a reply early. I'm also still waiting for Emory and Northwestern as well. Wishing us both good luck!