If traveling 65 MPH over a 20 mile distance instead of 55 MPH approximately how many minutes would you be saving?

65 mph = 1.083r miles per min

55 mph = 0.916r miles per min

therefore

20 miles @ 65 = 18.46 mins

20 miles @ 55 = 21.83 mins

so you save 3.37 mins, provide a constant speed, not including time to accelerate.