Mine was just approved 5 days ago. I first submitted it in July. Go to
the NFA Tracker website to get actual averaged out wait periods. I did the math on mine and it was pretty spot on accurate with the graph from the website.
You can also call the ATF at 304-616-4500 to get the status of your paperwork (you'll need your suppressor serial number), but they only say "it's in progress" or "it's approved". They don't tell you where you fall within the stack of other Form 1s or 4s.