The time periods specified herein are maximum time periods only, and are not meant to indicate the time expected to be necessary to review the average application. These time periods may be extended by mutual consent between either the Technical Review Committee or the Planning Board and the applicant. However, in cases where approval by the Zoning Board of Review is not required, failure of the Planning Board to act within the periods prescribed herein shall constitute approval of the Development Plan and a certificate of the Administrative Officer as to the failure of the Planning Board to act within the required time and the resulting approval shall be issued on request of the applicant.