Prisoners sentenced to imprisonment for violations of offenses identified in § 42-56-24(a) and (b) shall be eligible to have deducted from his or her sentence up to three (3) days per month up to a maximum of thirty-six (36) days per year, when in the determination of the director, or his or her designee, an inmate has performed heroic acts affecting the lives and welfare of the institutional personnel, inmates, or the general public, or when an inmate has submitted extraordinary and useful ideas and plans which have been implemented for the benefit of the state resulting in substantial savings and/or a higher degree of efficiency or performance while participating in and completing academic or vocational education programs, or when an inmate has submitted useful ideas concerning academic or vocational programs which have been implemented at the adult correctional institutions. Nothing in this section shall be construed to deprive a prisoner of time already accumulated or deducted prior to May 8, 1974.