Are you certain about the 90 days still existing? I thought it was replaced completely with the new infinite time period providing you and the PD do their parts prior to expiration.
G.L. c. 140, § 131(i)
For the purposes of section 10 of chapter 269, an expired license to carry firearms shall be deemed to be valid for a period not to exceed 90 days beyond the stated date of expiration, unless such license to carry firearms has been revoked.