As a PPL I can only imagine a few reasons for the LH wanting to over ride the RH pilot. In all the reasons I can think of, and I am sure that there are many more that wouldn't occur to me, 40 seconds seems an awfully long time to have to press the over ride button. When things are going wrong, they can get a lot worse in that time.
May I ask what is the logic for choosing 40 seconds?