In harmony with the general purpose and intent of this Resolution and the general purposes of the Special United Nations Development District and in accordance with the provisions of this Chapter, the existing district regulations are superseded and replaced by the regulations applying to a C5-3 District, except as modified by the provisions of this Chapter, for construction of any development in the Special United Nations Development District, provided that the development is undertaken in accordance with a development plan approved by the City Planning Commission and the Board of Estimate, which plan comprises zoning lots having a total area of at least 1.5 acres to be developed at one time or in stages, and that such development is undertaken by or with the consent of the party proposing such plan, and further provided that the Chairperson of the City Planning Commission certifies:

(a)        for development commencing before January 1, 1980, that the final plans generally comply with the design concept dated January 6, 1970, on file with the Commission; or

(b)        for development commencing after January 1, 1980, that the final plans generally comply with the amended design concept dated April 30, 1980, on file with the Commission.