Downtown along 7th Ave. from the time the light goes from "walk" to a red light is about 5 seconds (if the countdown clock is accurate). That's enough time if you quicken your pace to get across, if that light just changed when you stepped out on the crosswalk. Obviously in that situation the best move is to not try to cross, but if you had mobility issues and were on the crosswalk already then you could have a problem.