From and after its adoption, these regulations shall govern each and every subdivision of land within the corporate limits of the City as now or hereafter established. Preliminary plats approved under subdivision regulations in force and effect prior to its adoption, shall be governed by the regulations in force and effect at the time of preliminarly plat approval and shall become null and void at the expiration of the time period called for in these Subdivision Regulations. The applicant may submit on or before the expiration of this period, the whole or any part of the preliminary plat for final approval, and at that time, the time for filing such final plat may be extended by the Commission. The City Planning Commission shall have final approval of all plats.