In M1-5B Districts, the City Planning Commission may, after public notice and hearing and subject to Board of Estimate approval, permit modification of paragraphs (a)(3), (a)(4) and (b) of Section 42-325, provided that the Commission finds that the owner of the space, or a predecessor in title, has made a good faith effort to rent such space to a mandated use at fair market rentals. Such efforts shall include but not be limited to: advertising in local and citywide press, listing the space with brokers and informing local and citywide industry groups. Such efforts shall have been actively pursued for a period of no less than six months for buildings under 3,600 square feet and one year for buildings over 3,600 square feet, prior to the date of the application for a special permit.