When you begin to learn the importance of timing and how it effects your results, you will hear the saying "Dance with the pitcher". At the MLB level some players change their walk up music to match the rhythm of the pitcher to help with this dance.
What this means is like a dance your movements need to one with each other. To early or to late and the dance is ruined. It's the pitchers job to disrupt this sync and the hitters to stay on it. The one who succeeds at this goal wins the battle of that pitch.
To do this a hitter needs to begin his load as the pitcher is separating his hands, a negative move will instantly allow the timing to be off (very common in lower level hitters). The act of the "LOAD" is commonly misunderstood. You are behind in the dance, pop up.
Next as the pitchers hips begin to come forward so should the hitters, getting your foot down early also breaks the sync. This makes the hitter early, weak ground ball.
Then based on the pitchers velocity your foot should hit the ground about the halfway point of the balls flight as by now you have identified the pitch and decided how to act not react.