To elaborate on what has already been stated:
The slowest speed an aircraft can safely travel is (just above) its stall speed. For most smaller commercial jets the stall speed with flaps up is going to be around 150-160 KAIS and with flaps down around 120 KAIS.
The cruising speed of the aircraft is typically going to be calculated to optimize fuel performance at a given altitude and for smaller commercial aircraft that is going to be in the 400-450 KAIS range for a 30,000+ft cruise. If the trip is only 150 miles you might only go into the 20,000ft range.
As has already been pointed out, if you are going of listed departure/arrival times then that one hour is broken up like this: 12 minutes between leaving gate and takeoff, 15 minutes of climb, 5 minutes of cruise, 20 minutes of descent to landing, and 8 minutes to taxi to the gate at arrival.
So in a 1 hour "flight" only 5 minutes was spent at the cruise speed and only 40 minutes was spent in the air. And that is a little generous, from my experience the airlines budget 30 minutes of listed flight time for time spent on the ground.