You should have time but be sure to allow at least one hour travel time to/from JFK and arrive back at JFK at least 2-3 hours before international departure. Easiest and most direct to Manhattan is taxi; $45+tolls+tip each way. Cheapest is by public transportation; AirTrain from terminal to Jamaica Station and either subway or LIRR to Manhattan. AirTrain/subway is $7.25 each way and LIRR a bit more but faster.
You should have time but be