There are no "hours" in any distance. If the question is really "How long would it take to travel 721 miles?" then the answer depends on the average speed, which depends on the mode of travel.
721 miles
Detroit to Michigan is roughly 721 miles.
448 MI/ 721 KM
It is 721 square miles.
721 miles
721 miles
how many is 260 miles
698 miles through Springfield 721 miles through St. Louis
3 hours 1.7 minutes
0.0833... hours.
At 60 miles per hour, six hours. At 30 miles per hour, twelve hours.