Please know that 20 times roatation is an approximate count. Rotation also depends upon the quantity of the liquid/water/food.
Know that as the given quantity of water is full with the energy sent, the energy makes a repulsion. It can tell you when to stop rotating. Try to experiment and share the result. It may not or may take time for you to know the result as it depends upon a healer ( new or a old healer) also. How sensitive the healer is.