The way that Excel stores times is as fractions of a 24-hour day. So
the time 12:00:00 would be stored internally as 0.5, and 6:00:00 as
0.25. So, if you divide miles directly by the recorded time, you would
have miles per day - if you want miles/hour you must also do a further
division by 24, and if you want miles per minute then you would divide
by a further 60.

Let's say a car does 60 miles/hour. Then in one minute it will only
travel 1 mile. In one day (assuming no stops for petrol etc) it could
travel 1440 miles (24 x 60)

Hope this helps.

Pete