You don't need to drive through the heart of NYC to get to JFK? The airport's on Long Island. That'll be a tight ride though. New Haven to the Throgs Neck Bridge (to Long Island) will take a good hour at ~70 mph. You'd be driving with the afternoon rush so it'll be busy throughout your route, especially as you near NYC. I think you'll be ok as long as there isn't a major accident somewhere along your route. Oh, and you'd have to go through the cash lines for the tolls (you don't have an EZPass right?) so that's always hit or miss. My feeling is that 3h should be plenty barring major accidents or closures (which aren't uncommon). I've done that drive many times and even in a snowstorm at night it didn't take longer than 3h to drive that distance. But definitely get some other opinions.