The "chasing" process varies. At its shortest, the chase can last a few days, but it can also last up to a week or more. The chase itself will only last a few hours each day.
The chase is part of the fish's spawning process. The male fish will chase the female fish until she releases her eggs into the water. Then, the male will fertilize the eggs while they are in the water. The timing of the chase will depend on the temperature of the water. The male will chase before the temperature gets too high (usually 1:00 or 2:00 PM), and after the chase, the fish will return to normal behavior.