Getting there on time is one of my many weak points. Not only because of poor footwork (which I'm working on) but also because I'm totally not good at predicting where the ball is going to come. When I'm blocking I stay close to the table so my reaction time limit is very little. To deal with it I should learn to predict the incoming ball but I have no idea of how to do it. I guess I should just wait and with experience this will come too.
So, hopefully this information is helpful. This is about technique and it is hard to learn to do this, but to get to higher levels, you have to be able to do this. If you are trying to predict where the next ball is going and you are feeling like your reaction time is slow, you are probably missing a huge piece of technical information and know how.
When you are in a rally, you need to be reset and ready for the ball to move in any direction (FH or BH, in or out) before your shot bounces on the other side. Then, from a ready position, you need to be watching the ball and the angle of the opponent's racket as the opponent is making contact so you can see,
as he hits the ball, where the ball is going. Then you are not predicting where the next ball is going, you are seeing where it is going
as the ball is being hit. When you do this, you have much more time to move to the ball. When you are trying to move to the spot of the ball even after the ball is only an inch off the opponent's racket and you did not fully watch the racket angle and contact, you are going to be in big trouble.
To be reset before your ball bounces on the other side is really hard and it takes a lot of technique. That is why so much of the technique at mid-level play is about learning to use compact efficient strokes.
However, with blocking, it should be easier to reset because it is a block not a stroke. So when you block you just need to get into a ready position for the next ball as fast as you can. You are still watching your ball after you hit it, but you have to get reset ASAP. Some people watch the ball but do not reset. Without a fast reset it is really hard to be in position to move to the next ball.
As you work on this, you probably should get someone to do some random ball placement drills with you. These help because they get you to start watching the ball off the opponent's racket better and to move to randomly placed ball at a speed you can handle and keep form. As you get better, the drills get faster and harder.