As I understand it, the Federal discount is 15% for good behavior which, in his case, would probably include not being caught masturbating, a difficult rule for him to comply with in the fairly open setting of a minimum security facility where the inmates are often placed in cubicles, not cells.
21 month sentence, doesn’t report until November, time off for good behavior, take advantage of programs that serial sex offenders are offered, and he will be out in less than 12 months. What a farce.