Approval of a development plan shall expire 180 days from the date of approval unless an application for a building permit or certificate of occupancy has been filed within such period, or, in the case of a use permitted by variance or special use permit, within such period application is made to and diligently pursued before the Zoning Board. Denial of such building permit or certificate of occupancy, on grounds unrelated to the development plan review, shall not affect the validity of the development plan review approval, provided that a building permit or certificate of occupancy is eventually issued no later than 180 days from the date of development plan review approval.