Except as provided in subsection (b) of this section, a public–private partnership agreement may not exceed 50 years, including all renewals and extensions. The Board of Public Works may: waive the prohibition set forth in subsection (a) of this section if the Board determines that the reporting agency has demonstrated sufficient reason for the agreement to have a longer term; and waive the prohibition set forth in subsection (a) of this section at any point during the presolicitation, proposal review, or agreement negotiations process.