The only straightforward way to modify the duration is to use the DIP switches– that is what they are there for. If you need two different delay times, you will likely need to either
(1) reprogram the microcontroller to add an additional, fixed delay time,
(2) use a second Art controller, with its DIP switches configured to give the other delay time, or
(3) provide an external signal or delay that halts or triggers the Art Controller at the appropriate times.