Visit flightaware.com and type in NWA#### (#### is the flight number) and see what it says for flight times. These are actual wheels-up-to-wheels-down timings as recorded by radar.

I looked at several when I replied earlier today and I'll stand by my statements that "the flight from JFK-DTW is about 1:15 to 1:30; really, it's not that bad. The return DTW-JFK is just over an hour."