About 45 days. Submitted 5/5 and signed 6/19. Rec'd 6/23.
I filed one for moving my cans from SC to PA. Current regs require you to INFORM ATF of a change in location in writing for silencers. Last year they started ASKING us to do so with silencers by submitting a Form 20.
Since we are only required to INFORM them, not get authorization, I didn't wait for the return but kept a copy of the submitted form.