The Two Secrets of Timing
Of all the things I'll point out during the course of a day of tennis instruction, late swings rank right at the top. These late swings happen for a variety of reasons: your preparation is lax, your mind's focused on some mechanical aspect of the stroke you're hitting, you're distracted by your opponent or the part of the court you want to hit to, or you simply misread the variables of the approaching ball.
These things can happen to anyone and at any level of play. But they are avoidable to a great extent. There are two things that I promote to develop better timing and all the beneficial things that come with it. These two factors work together. The first is the way you watch the ball. The second is a little formula I've developed that ensures hitting the ball on the rise.
Like pretty much anything else in tennis, when it comes to truly incorporating these elements into your game, be prepared for loads of disciplined, patient practice. If you put the work in, the prospects for a substantial improvement in your groundstroke timing are very good.