Good to keep it going till the water looks clear and the OCLT (overnight chlorine loss test) shows a loss of <1.0 FC when initial test is after dark and the final test is the next day before sunlight hits the pool.
It's not counted in days. If you stop too soon, you'll either prolong your agony continuing the SLAM or your pool will turn green after a period of time. If you follow TFP methods, you won't have to worry about a green pool (unless you colored it that way) LOL
Study this: Perform the Overnight FC Loss Test (OCLT) - Trouble Free Pool
It's not counted in days. If you stop too soon, you'll either prolong your agony continuing the SLAM or your pool will turn green after a period of time. If you follow TFP methods, you won't have to worry about a green pool (unless you colored it that way) LOL
Study this: Perform the Overnight FC Loss Test (OCLT) - Trouble Free Pool