Pitches don't suddenly move or change speeds! Physics dictate that EVERY pitch (except, and then only on rare occasion, a knuckeball) follows a smooth trajectory (i.e., there are no sudden drops, rises, or breaks) with the velocity decreasing gradually following release from the hand (i.e., there are no drastic changes mid pitch). If you're really interested in the physics, use the DFP search function to find posts by POBguy.
That was pretty well debunked as all his data shows the relationship over distance, not time. When he finally plotted the pitches by time the result was different.