The county planning commission shall act to approve or disapprove a subdivision plat within 30 days after its submission; otherwise, such plat shall be deemed to have been approved and a certificate to that effect shall be issued by the county planning commission on demand; provided, however, that the applicant for the commission's approval may waive this requirement and consent to an extension of such period. The grounds for disapproval of any plat shall be stated upon the records of the county planning commission. Any plat submitted to the county planning commission shall contain the name and address of a person to whom notice of a hearing shall be sent, and no plat shall be acted on by the commission without a public hearing thereon. Notice shall be sent to the said address by registered or certified mail of the time and place of such hearing not less than five days before the date fixed therefor. Similar notice shall be mailed to the owners of land immediately adjoining the platted land as their names appear upon the plats in the county tax assessor's office or on the tax records of the county. Approval of a plat shall not be deemed to constitute or effect an acceptance by the public of any street or other open space shown upon the plat.