The plat shall be approved or disapproved within ninety days after submission thereof; otherwise such plat shall be deemed to have been approved and a certificate to that effect shall be issued by the council on demand; provided, however, that the applicant for the approval may waive this requirement and consent to the extension of such period. The ground of disapproval of any plat shall be stated upon the records of the council.
SDCL 11-6-32