It depends on your examiner as well as many other things like how long it takes FBI to get your prints back.

My advice is if you are concerned with a time limit don't ever think about NFA weapons. You simply submit the paper work and wait a month then check to see if it's pending. After that you forget about it and when it shows up it's a surprise.

Since ATF moved they have been much faster for some people and not others it realy depends. You are rolling the dice nobody can say.