They have been running behind, so I'd recommend that you apply 60 days before expiration. By statute, the issuing authority has 7 days to submit to the State, then the State has 30 days to respond, and the entire process must be completed within 40 days.
You will receive a notice from the FRB approximately 3-4 weeks prior to expiration. It states "Be advised that Chapter 150 of the Acts of 2004 provide that if the holder applies for renewal prior to expiration of the LTC or FID card, it will remain valid for a period of 90 days after the stated expiration date, unless the application is denied." I'd suggest getting a receipt for your application, and good luck buying firearms or ammo until your new license arrives.
PS: I applied for renewal 60 days ago - nothing yet.