Griffen was born on March 13th, 1998. He turned 21 on March 13th, 2019.
An athlete can play professional in North America, or in Europe, and maintain their full 5-year eligibility provided participation takes place prior to (before) December 31 of the year the athlete turns 21. In this case, if he played professional starting January 1st, 2020 he would be hit with i) a year of eligibility and ii) the 365 days of rest.
Griffon started the season in the ECHL after being cut from the Moose. After six games, he was recalled by the Moose, but return to the ECHL on December 31st. He subsequently played 10 more games up to January 25th when he left at the beginning of the 3rd period, versus the Florida Everblades, with an apparent lower body injury.
Having played professional in January 2020, he loses one-year of eligibility and with his last game on January 25th, the 365-days of rest means he is not eligible until January 25th, 2021.
Unless the team has some injuries, I would see him practicing and starting for the 21-22 season as a replacement for Rylan Parenteau.