Except as provided under section 12.1-32-09.1, an offender committed to the legal and physical custody of the department of corrections and rehabilitation is eligible to earn sentence reductions based upon performance criteria established through department and penitentiary rules. Performance criteria includes participation in court-ordered or staff-recommended treatment and education programs and good work performance. The department may credit an offender committed to the legal and physical custody of the department who is eligible for sentence reduction five days good time per month for each month of the sentence imposed. The department may credit an offender with sentence reduction for time spent in custody before sentencing and commitment to the legal and physical custody of the department. The department may not credit an offender with any sentence reduction for time spent on probation under the supervision and management of the department.