Biding time @ JFK

I've a six hour layover this Saturday at JFK, and thinking that's too long even for a SC stay.

What's a realistic transit time into Manhattan, for example? Would an hour each way do? That'd leave us a few hours to hang out, maybe get an early dinner.

And as long as I have you on the phone, what's the most efficient way to get to Manhattan from JFK?

Thanks.