The best timing for saving shots, either for penalties or in open play, is to dive (R + direction) just before the opponent is about to shoot. During penalty shoot-outs, this is the optimum time to dive as it will give you an animation that covers the most amount of distance and makes scoring the penalty very difficult. Watch out for penalty takers stuttering, though, as this may make you mistime your save and reduce your chances of keeping the ball out of the net.