With a margin of error of 10 minutes , Old Faithful will erupt 65 minutes after an eruption lasting less than 2.5 minutes or 91 minutes after an eruption lasting more than 2.5 minutes .
With an error of 10 minutes , Old Faithful will erupt 65 minutes after an eruption lasting less than 2.5 minutes or 92 minutes after an eruption lasting more than 2.5 minutes .