It pretty much sets the colors immediately once you put it into the basin. I have had a couple batiks fabrics run a little more. But, I continue to treat it until the cold rinse water runs clear. The darker the dye and the more dye baths they use make the diference on how much dye they have put into the fabric. Some are so overdyed that the fibers couldn't hold the extra they put on it. See what I mean?
There is a bottle of fabric setting solution that is called retain. I bought some before reading the label. It has a caution that it might cause cancer on it! Needless to say, I wasn't gonna use that! No way!