Turnaround time was really good when Ken Houchens was at the helm of NFA (I had a few transfers go 30 days, mailbox to mailbox), but unfortunately, Ken has moved on. Probably fired him for being too competent and efficient to work at BATFE.
My last few transfers have been in the 90 day range (spring/summer this year). I've got one or two cooking which are currently at about the 70-80 day mark. If you get 90 days without approval, give NFA a call and check status. Prior to Houchens, 90 days was an average, with some going 120 or longer. I've had one or two go to about 270.