After adoption of subdivision regulations by the governing authority, the local commission is hereby given the authority to give tentative approval or disapproval to preliminary plats and to approve or disapprove final plats but in each case their action shall be taken within sixty days after the submission thereof; otherwise, such plats shall be deemed to have been approved and a certificate to that effect shall be issued by the planning commission on demand; provided, however, that the applicant for the planning commission's approval may waive this requirement and consent to the extension of such period. The grounds of disapproval of any plat shall be stated upon the records of the planning commission. Any plat submitted to the planning commission shall contain the name and address of a person to whom notice of hearing may be sent; and no plat shall be acted upon by the planning commission without affording a hearing thereon, notice of time and place of which shall be sent by registered or certified mail to said address not less than five days before the date fixed therefor.