From dusk till... Don?

From Stephen Sondheim's Finishing the Hat:

To me, a native New Yorker, "dawn" rhymes with "lawn" and "gone" with "on." When I worked with Leonard Bernstein, who was born near Boston, he insisted, to my horror, that all four words rhymed with each other. For a musical version of "The Boston Strangler," that might have been acceptable. For a show about New York street gangs, it was not.