Columbia was one of the quickest responces I got. After my app was sent out, I would guess it took them 4-5 weeks to send me an invite letter (AADSAS took forever to send my LORs and transcripts after my application).
BUT, when I did get the invite, they didn't have dates available to interview for 5-6 weeks out. I actually just got back from there this weekend. I really liked the school. But I've really liked every school I've been to. I hope I don't get into some of them so my decision will be an easy one.