Last report I saw on here was 2 - 3 months, I think.

When you are approved, it also can't hurt to just check to see if they'll take you as a walk in the next time you're flying. I've seen reports of this working sometimes, I'm guessing if its not a busy day or people with appointments no show (this does happen). By no means is it a guarantee, but if you're going to fly anyway, it might be worth a shot. You'd need to get to the airport earlier for your flight, of course, as it takes about a half hour to go through the process, and you'd have to bring your approval letter and your id.

Also, I'm not sure if all of the city/land border offices have iris scanning equipment yet, but at least some of them do, and they are reported to have shorter waiting times.