"In a hot New York minute. Immediately. Equates to a nanosecond, or that infinitesimal blink of time in New York after the traffic light turns green and before the ol' boy behind you honks his horn. Or you could define it like this: the imperceptibly brief moment between when you open your mouth to speak and a New Yorker interrupts you."
Charles Harrington Elster, What in the Word? Wordplay, Word Lore, and Answers to Your Peskiest Questions about Language (Harvest Original)