Upon receipt by the Department, persons who have been confined while awaiting transfer to a state correctional facility shall be credited with such time as is certified to the Department in accordance with §§ 53.1-116 and 53.1-129 and as is otherwise provided by law. Certified good conduct allowance shall be applied to reduce the person’s maximum term of confinement, and one-half of such credit shall be applied to reduce the period of time the person shall serve before being eligible for parole. After admission to a state correctional facility, a person shall be credited at the rate of fifteen days for each thirty days of time served with satisfactory conduct. The person shall remain in this credit level until classified in accordance with § 53.1-201.