Construction or occupancy if no construction is involved, shall commence within one (1) year of the approval of the site plan and a certificate of occupancy issued within three (3) years of approval. If construction or occupancy is not commenced or a certificate of occupancy issued within these limits, the site plan approval shall be null and void. Prior to the expiration of site plan approval, the Planning Board or Site Plan Review Committee may extend these time limits upon written request of the applicant and a finding that such extension is consistent with current zoning requirements.