For developments, enlargements or other alterations within the Special Midtown District, any building permits issued by the Department of Buildings prior to April 28, 1988, shall continue in effect through May 12, 1988. Thereafter any non-conformance or non-compliance with the Zoning Resolution as so amended shall be subject to the provisions of Section 11-33 (Building Permits for Minor or Major Development or Other Construction Issued before Effective Date of Amendment).