Except as provided in subsection (c) of this section, a majority of the members of the review panel is necessary to make a decision. The review panel shall make the decision within 30 days after the filing date of the application for review. A review panel may not order a decrease in a mandatory minimum sentence unless the decision of the review panel is unanimous. A review panel shall consider time served on the sentence under review to be time served on any sentence that is substituted.