Special permits granted under § 410-4.3, Flexible plan development, of this zoning bylaw shall remain in effect for a period of two years plus such time required to await the determination of an appeal referred to in Massachusetts General Law, Chapter 40A, Section 17 from the grant thereof, and shall automatically lapse if a substantial use thereof has not sooner commenced except for good cause as determined by the special permit granting authority following a public hearing with proper notice per Massachusetts General Law, Chapter 40A, Section 12 or, in cases where a permit for construction has been granted, if construction has not begun by such date except for good cause as determined by the building commissioner.