This is two questions here, so I will answer that one first. We're just encouraging you to do it for those beings that may die while you are walking. You could also, if you wish, add any of them who get injured while you are walking, that's a little more. But just while you're walking, while you're doing it.
This type of activity of reflecting before your action you can add it into your other activities in your life if you have activities which cause death. We teach all the assistants, and we do it ourselves, that before we do activities which might cause harm - even if it is just sweeping - we tell them do the wish then, too, because it may cause harm. You can apply what we are telling you to do for the walking to other parts of your life.