No grant of a variance shall be valid for a period longer than six months unless such permitted use is established within such period, or in the event such permitted use is dependent upon erection or alteration of a building, unless a building permit for the erection or alteration is obtained within such six-month period; provided, however, within such six-month period the board may, upon motion of the applicant for such variation and without further notice, by order, extend the time period not exceeding six months; and provided further, that in no event shall any order of the board be extended for a period greater than eighteen months from the date of the first order of the board in any case where a building permit shall be obtained for the erection or alteration of a building unless such erection or alteration shall be started and proceed to completion in accordance with the terms of such building permit. (Ord. 1191-21 §13 (Exh. C), 2021).