Conditional approval of the preliminary layout shall be effective for a maximum period of 12 months, except that submission, within this period, of a final plat applying to a portion of the area covered by the preliminary layout shall extend the effective period of conditional approval to a maximum of 24 months from the date of submission of the preliminary layout. If a final plat has not been submitted to the plan commission within these time limits, the preliminary layout shall again be submitted to the plan commission for conditional approval.
('69 Code, App. B, § 4.8)