Expiration of a variance or special use permit

A variance or special use permit shall expire one (1) year from the date of granting by the board unless the applicant exercises the permission granted or receives a zoning permit to do so and commences construction or use and diligently prosecutes the construction or use until completed. The board may, upon application therefore and for cause shown, grant an extension, provided that no more than one (1) extension for a period of six (6) months be granted. Provided, however, where subsequent approval is required by the planning board the time shall not commence until final planning board approval, provided the applicant diligently pursues the application before the planning board and provided, further, that the process before the planning board shall be completed within two (2) years of zoning board approval.