"Tipping your pitch" happens long before the arm even begins to finish. Tipping comes much earlier; where the pitcher sets up on the rubber, amount of backward arm swing, direction of stride, intensity of leg drive, change in voice tone (for the grunters) - and many more. All the little things a pitcher does up to the delivery point can definitely give away a pitcher's tendencies. However, the finish of the hand/arm isn't evident until the ball has reached a point in it's flight where the batter must make a "to swing or not to swing" decision.
This is where style comes into play. Things like hiding the grip and making every pitch appear identical to the batter. It may be a great theory, but IMO, if girls could base a decision to swing on arm finish, you would see a dramatic increase in BA against the top women pitchers in the world. I think the practice time could be better spent disguising everything up to and including the release.