It varies from three days to three weeks. The total time depends on how diligent you are, how much risk you are willing to take, and a little luck. At one point, if you go too quickly the stains can come back. At another point you need to test and add chlorine a number of times with at least an hour in-between. And there is a risk of getting algae and not being able to raise the FC level enough to be able to fight it properly for several days.