The "Minimum trigger duration" sets the amount of time audio samples are saved when the amplitude of a signal goes over the threshold. This could be useful if you wanted to record the decaying tail of a loud impulse, such as a gunshot, or to record the quieter calls in a whole bat pass.
For the gunshot example if you selected a "Minimum trigger duration" of 0s with a 50% amplitude threshold it would only record the samples that go over 50%.
However if you selected a"Minimum trigger duration" of 2s with a 50% amplitude threshold it would record the 2s of the gunshot after the triggered event, which might include important information, such as the quieter tail as the impulse sound decays.
I hope that answers it.
Thank You Andy, now it all makes sense !!!!!!!