The final plat shall conform substantially to the sketch plan as approved and, if desired by the subdivider, it may constitute only that portion of the approved sketch plan which the subdivider proposes to record and develop at that time; provided, however, such portion shall conform to all requirements of the regulations set forth in this chapter. Subsequent final plats covering the remaining portions of the sketch plan shall be submitted within 24 months. Council may approve extensions upon recommendation of the Commission.