I drive from Niantic, CT down to LGA somewhat often. From HVN to LGA is about 2hrs on a Sunday with no traffic.
95 down to the White Stone Bridge and follow the signs.
You can also take Amtrak into Penn Station (I prefer it to Metro North) then cab it. I don't always finds the trains the most reliable form of transportation though.
HVN to JFK is much easier.........