How far would a tortoise move in half a day if the tortoise moves approximately 0.2 mph?

As you have indicated, the tortoise moves 0.2mph, which is equal to one fifth of a mile in one hour. One mile will be traveled by the tortoise in five hours. Half a day is 12 hours, so 0.2 x 12 = 2.4 miles.

A tortoise, traveling at 0.2 mph would travel 2.4 miles in half a day.