Timing is everything. IMO speeding up the swing according to the type of pitch is asking for trouble. Machines have it's place but nothing beats live pitching if possible. With higher velocity pitchers the batter has fractions of 1 - 2 seconds to read the pitch, the location, anticipate where the ball will be once it crosses the plate, and decide to swing or not. My son mentioned he studies the pitcher's mechanics and tendencies several batters ahead of him if possible and throughout the game. From my recollection he starts his body (swing) motion at different throwing release points depending on the pitcher. It should be noted though that his body motion is to the extreme, lots of movement. He gets away with it (so far) by having very good timing and quick hands. Upon contact though his feet are down, proper weight transfer, body position, and swing path. For your son, find the correct timing tool and practice it until it becomes part of his muscle memory. HIs hitting coach can help with this. Best of luck!