Dependson the polish, how much of it you use, and how hard and long you press on it with the spinner.
There are basically 2 classes of polish: those with grit in them and those without. Those without will not change the grit; so yo uhave what yo ustarte dwith, just more length.
Complications arise when you use a polish with grit in it. Just because the polish is labeled 2000 grit does NOT mean no matter how much you apply and how hard you press and for how long you press that they will make all balls 2000 grit. It all depends on how much grit is actually in the polish, how much polish you put on the towel or the ball, how hard you press (some labeled 2000 grit can take the ball down much further to 3000 or more grit), and how long you press on the ball, while it's spinning. Get the picture?
There is no cut and dried formula that you can plug numbers into.
The best you can do is experiment with what is good for you and your reaction, on the lane surface and oil pattern on which you bowl. Try to be consistent in your polish application.