If after a zoning permit or conditional use permit has been authorized by the Zoning Officer or Land Use Board, the applicant has not obtained the permit within a period of six (6) months from the date of such authorization or as provided by N.J.S.A. 40:55D-1 et seq., then such authorization shall be null and void, and no permit shall be issued there under unless the applicant shall have, prior to the expiration of the aforesaid six (6) month period, made written application for an extension. Such extension shall be granted by the appropriate approval authority, for a period not to exceed six (6) months, upon good cause having been shown by the applicant.