The 300 minutes that the inmate gets to use on a per month basis resets the same day every month by the BOP, however, that date is different for each inmate. The Service from InmateAid recharges every 30 days for only $5.
https://www.inmateaid.com/ask-the-inmate/with-the-bop-discount-phone-line-300-mins-per-month-if-you-use-up-the-300-minutes-before-the-month-is-over-will-i-have-to-wait-until-after-30-days-to-make-another-purchase#answer
Accepted Answer Date Created: December 30,2019