I believe that in the beginning of training a student should try not to breath during a movement in kata. This allows them to concentrate on the packing of the breath when still and the actual movement separately. The hope is that they will learn to keep their breathing down at all times. However, once you have obtained some skill at keeping your breathing down, then this loses importance.
As you progress and learn to maintain that protective breathing without conscious thought. You should then, as Van Sensei said, simply breath when you need to. You can also breath to serve a purpose. To breath out deliberately during a movement can harden it. To breath in deliberately during a movement can soften it.