The surge can last up to 72 hours, I usually only get one strong positive but had 2 this month too. They say to stop testing after the first definite positive, I kept testing because I've not been using OPK's/getting results from them for too long so i wanted to make sure what a positive looked like cos I think I've thought ones were positive before but if I'd kept testing they would have went darker and I'd of known better x