Not sure that the pause in the breathing cycle is a full 3 seconds, but there is one there. In fact if you ever shoot a pistol or rifle, during that pause is when you should pull the trigger, that's when your body is most relaxed and there's less of a wobble effect
. How does that translate to diving? Well you can carry that over to when you press the shutter for photography assuming all the bubbles are out of the way! It's also better since your're not breath holding and rising when taking a picture, providing more stability when you snap that shot.
Cheers and Safe Diving,
R