Here's the problem with that thinking. The pitch speed is calculated as it leaves the hand, not from the mid point or end point (or some other random point) in its travel. Nor is it deduced by the total travel time from hand to catcher's mitt.
Any pitch will slow with distance as the lack of continued force being imparted, wind resistance, and gravity take its toll. The ball thrown from 46 feet will slow less than the pitch from 60, maybe a mile or two per hour. Reaction time from 46 feet is therefore, obviously, shorter than from 60. However, that wasn't the question.