I think that given the 'duration' setting, the author made sure that the event would take place in a given time, constraining the problem. Edit: that being sai

I think that given the 'duration' setting, the author made sure that the event would take place in a given time, constraining the problem. Edit: that being said, it looks like in the heavily damped case it takes much less than the full duration to finish. That is probably a bug.