100 minutes are added to the normal 300 minutes during the November-December holiday season in the federal prison system only.
https://www.inmateaid.com/ask-the-inmate/if-my-husbands-phone-time-cycle-starts-on-the-28th-of-each-month-how-does-the-novemberdecember-400-minutes-work-does-he-already-have-the-400-minutes-or-will-they-add-a-hundred-minutes-november-and-december-1st.amp#answer
Accepted Answer Date Created: October 30,2013