When calculating for a low-flow fixture, it is required to enter a duration (which is default set to 30 seconds). There is a footnote that says "Duration may be modified for special circumstances". I have no idea what this means. It makes sense that a metered faucet would have a duration, but a low-flow fixture just runs for as long as needed (probably like 12-15 seconds each use). When I calculate total water reduction with low-flow fixture duration set to 30 seconds, I do not hit the 20% reduction needed for the prerequisite. But when I change the duration to 15 seconds, I can hit the 20%. Is it ok for me to change the duration?