(a) The Commission shall issue its decision within 90 days: After it receives the appeal brief; or its ruling on a request for intervention, if applicable; or after the conclusion of briefing by the parties, whichever comes later, unless the subject of the appeal is whether to dissolve or make permanent a temporary closure order issued under § 573.4 of this chapter, in which case, the Commission shall issue its decision within 30 days of conclusion of briefing by the parties.

(b) The Commission shall serve the final decision upon the appellants.