How long is the flight from Denver CO to Detroit MI in a Cessna airplane?

It depends what kind of Cessna airplane you are talking about. Cessna has made anything from a single engine 152 that has an airspeed of about 120 mph to a Citation X, a business jet capable of flying at mach .92 (over 600 mph), which is just under the speed of sound.

It is about 1150 air miles from Denver to Detroit, so the flight in a 152 would take 9.5 hours (not including stops for fuel or factoring in winds aloft), while the Citation X could do it in just under 2 hours non-stop.