The approval of a final development plan for a Residential Planned Unit Development district shall be for a period not to exceed five (5) years to allow for preparation and recording of the required subdivision plat and development of the project. If no construction has begun within two (2) years after the approval is granted, the approved final development plan shall be void, and the land shall revert to the district regulations of the district in which it is located. An extension of the time limit of modification of the approved final development plan may be approved if the Board of Zoning Appeals finds that such extension is not in conflict with the public interest. No zoning amendment passed during the time period granted for the final approved final development plan shall in any way affect the terms under which approval of the Residential Planned Unit Development was granted.