Before action on the Major Subdivision Plat - Final Plat or a Minor Subdivision Plat, if improvements are warranted by the Board of Supervisors, the applicant shall enter into a Development Agreement providing for the installation of all improvements in the subdivision required by the Ordinance and shall further provide a reasonable timeframe for completion of all improvements as required by the subdivision. No final plat shall be approved by the Board of Supervisors until such agreement has been fully executed.