I think one of the most important elements when looking at boiling times is Altitude. At sea level 1 minute of a rolling boil is acceptable, but 3 minutes is recommended. At elevations above 2000m (5000’) then 3 minutes is required and 5 minutes is recommended. The difference is just a 'fudge factor' because in wilderness conditions things go wrong and a little more time is better than a little less and everyone option on a rolling boil may be a bit different as well. Don't take chances boil your water for at least 3 minutes.