Well, so far. I went camping on the weekend of the first of this month. It is now the 10th and though some patches 'appear' to be healing new spots are popping up and spreading. What I've heard is that the areas that didn't get as much urishol will break out later than the first areas. Lasting...who knows, I've seen as much as a month and have heard longer still. It depends on your resistance so is on a personal basis. Plus the Urishol on for example camping gear can reaffect you long long long after it got on the equipment, so that should be washed too or you can get more, they say soap gets it off. I will be throwing away most of my tarps that were on the ground. Good luck!
