A site specific development plan shall be deemed approved upon the effective date of the final Board of County Commissioner’s action approving such plan. In the event amendments to a site specific development plan are approved, the effective date of such amendments, for purposes of duration of a vested property right, shall be the date of the approval of the original site specific development plan, unless the Board of County Commissioners specifically finds to the contrary and incorporates such findings in its approval of the amendment. Pueblo County is authorized, but shall not be required to extend vested property rights for a period exceeding three years where warranted in light of all relevant circumstances, including, but not limited to, the size and phasing of the development, economic cycles and market conditions and the like.