1. Approval of the site plan, including any phase of a multi-phased site plan, is valid for a period of eighteen (18) months. If actual physical construction of a substantial nature of the improvements included in the approved site plan has not commenced and proceeded meaningfully toward completion during that period, the approval of the site plan shall be null and void.

  2. Upon written application filed prior to the termination of the eighteen (18) month review period, the Planning Commission may authorize a single extension of the time limit for approval of a site plan for a further period of not more than eighteen (18) months. Such extension shall only be granted based on evidence from the applicant that the development has a likelihood of commencing construction within the extension period, the length of which shall be determined by the Planning Commission, but which shall not exceed eighteen (18) months.