In addition to any commutation or diminution of sentence or any meritorious time service award which may have been granted under § 18-7 or 18-7a, any inmate committed to the custody of the Commissioner of Correction for a definite term, or for a term with a minimum sentence imposed, may have not more than one hundred twenty days deducted from any one continuous term of imprisonment as an outstandingly meritorious performance award in the discretion of the Commissioner of Correction for exceptional personal achievement, accomplishment and other outstandingly meritorious performance, provided any serious act of misconduct or insubordination or refusal to conform to institution regulations occurring at any time during his confinement shall subject the prisoner, at the discretion of the warden and the commissioner, to the loss of all, or any portion, of any time awarded under this section. When any prisoner is held under more than one conviction the several terms of imprisonment imposed thereunder shall be construed as one continuous term for purposes of determining eligibility for any outstandingly meritorious performance award authorized by this section.