If a variance or special exception is granted, or the issuance of a permit is approved, or other action by the appellant or applicant is authorized, the necessary permit shall be secured and the authorized action begun within six months after the date when the variance or special exception is finally granted or the issuance of the permit is finally approved or other action by the applicant or appellant is authorized, and the building or alteration, as the case may be, shall be completed within 12 months of said date. However, upon written request by the appellant or applicant for good cause, the Board may extend either the six-month or twelve-month period, or both. In the case of an approval for a land development or a subdivision, the time period shall be automatically increased to 12 months to secure a permit and commence the work and 24 months to complete the work, unless approved differently under conditions attached by the Board.