All the times that I used to fly LGA-DTW and back, the flight time information that was broadcast over the PA system was about 1:10 or less. If you look at the flight schedule, just as with any other airline flying in and out of LGA, it's padded to take the waiting and cruising time around the tarmac to get in the takeoff line up into consideration.
JFK is more or less similar distance so it should not take much more than that.

HJ