(a) Issuance of opinion. In the absence of a determination of good cause for extension, the Commission shall issue an advisory opinion in proceedings conducted under this subpart not later than 90 days following the filing of the Postal Service's request for an advisory opinion.

(b) Special studies. Advisory opinions shall address the specific changes proposed by the Postal Service in the nature of postal services. If, in any proceeding, alternatives or related issues of significant importance arise, the Commission may, in its discretion, undertake an evaluation of such alternative or issues by means of special studies, public inquiry proceedings, or other appropriate means.