Any new proposed construction for which a zoning certificate is issued shall be commenced within six (6) months of issuance of the certificate and the ground story framework, including structural parts of a second floor or roof shall have been completed within one (1) year after the issuance of the Zoning Certificate; provided, however, that any project or building originally contemplated to be constructed in phases or for a period longer than one (1) year may be completed in phases or during such extended time if in accordance with a timetable placed on file with the Zoning Inspector with the original request for the certificate.