It took the city five years to rescue rotting East Midtown by rezoning it for 21st century office use. And it took architectural nitpickers barely a month to turn back the clock — trying to block plans to modernize the lower portion of 550 Madison Ave., the former Sony Building.

The charge against the project is led by architect Robert A.M. Stern, who wants the building landmarked. He calls the Philip Johnson and John Burgee-designed structure with a “Chippendale” top “an icon of Postmodern corporate design.”

In fact, architectural critics are as split on 550 Madison’s importance as the public is to its “beauty.” Not only that, the “icon’s” lower levels are not the 1980s “Postmodern” original. Sony in the 1990s replaced the original open-air sidewalk arcade with granite storefronts and enclosed the open atrium between East 55th and 56th streets.

The landmarks law is meant to protect and preserve buildings of clear-cut architectural and/or historical value. It wasn’t meant as a tool to thwart a redesign that one particular individual or group doesn’t like. Yet that’s what’s at risk of happening at 550 Madison.

It isn’t about zoning — the changes the owners want to make would have been allowed under the old rules. But denying them the right to redesign 550 Madison’s lower floors is diametrically contrary to the spirit of the new zoning — which, by allowing large new buildings to go up, is intended to stanch the exodus of great companies from East Midtown to the West Side and Downtown.