Friday afternoon in the summer is the worst time to be on the roads. In a "bad" case scenario it could take 2 hours to get to JFK, I would say 75-90 minutes is most likely, but an accident somewhere could really make it bad.
I would leave at 4pm, or even better, take the train, assuming you don't have a ton of bags. From UES, 6 subway to 51st St. to E train to Jamaica is probably your best bet.