Unless otherwise specified by the Board or by law, a variance, the subject of which does not require subdivision or land development approval, shall expire if the applicant fails to obtain a zoning permit within three months from the date of authorization thereof by the Board or by the court if such variance has been granted after an appeal, or fails to complete any erection, construction, reconstruction, alteration or change in use authorized by the variance approval within one year from the date of authorization thereof by the Board, or by the court if such variance has been granted after an appeal. Unless otherwise specified by the Board or by law, a variance, the subject of which requires subdivision or land development approval, shall expire if the applicant fails to obtain a zoning permit within 18 months from the date of authorization thereof by the Board or by the court if such special exception has been granted after an appeal, or fails to complete any erection, construction, reconstruction, alteration or change in use authorized by the variance approval within 30 months from the date of authorization thereof by the Board, or by the court if such variance has been granted after an appeal. The Board, upon written application and for reasonable cause shown, may extend the approval for an additional period of up to one year.