Conversely, I just did this in Atlanta a week ago yesterday (after not having enough time between layovers to do it in December), and I waited an hour and a half before making it to the head of the line — and then, only a little faster because the lady in front of me had waited longer than the 760 days or whatever after conditional approval to have her interview, so her application was expired and she was sent away.
In Atlanta, at least, they make you go through the regular immigration line first, and only then can you even join the Global Entry interview line. The whole thing took me well over two hours, probably more like 2.5.
I was happy enough, and I walked away with my approval, but it's not always a walk in the park (remember this was my second time trying this way since I don't live in the States).
(And the sole interviewer working in Atlanta that day — and yes it was a Saturday — was there because he was working overtime. So if he hadn't volunteered for OT, I guess there wouldn’t have been any interviews at all.)