Subdividers shall submit required preliminary plan materials and supporting documents of a proposed subdivision at a regular meeting of the Board for approval prior to the submission of a final plat. A receipt shall be issued to the subdivider for the preliminary plan submission.

     Approval of the preliminary plan shall be effective for eighteen (18) months. Thereafter, approval of the preliminary plan will have expired unless a final plat has been submitted to the Board within that eighteen (18) months, or a mutually agreed upon extension has been granted by the Board. Whenever, a final plat is submitted for less than the entire area covered by the preliminary plan, approval of the preliminary plan for the remaining unplatted area shall be extended for an additional eighteen (18) months.