I've heard different. I've always been told a 5 minute rolling boil kills whatever you need it to. The old way of boiling it for so many minutes, then adding 1 minute for every 1000' of altitude took too much to think about, and you MAY not know what your altitude it. So, keeping it simple (K.I.S.S.) is 5 minute rolling boil at ANY altitude. that should kill anything.
But, I also agree that, in a short term survival situation, if you have alternate methods for purification, use those. Takes less time, and, with tablets, you dont have to sit around & watch. Add, shake, wait, done!