I think that you are absolutely on the right track as far as when you are taking them on your workout days.
As far as non workout days go, the best thing to do, IMO, is to have one in the morning within a half hour of waking up and if you want a second one, go for it. I honestly don't think the timing is that important. You really need to listen to what your body wants if you are craving more food. DO you want carbs, sugar, etc... There are healthy foods that will solve those needs. If your body wants protein have another shake. I don't think that you will be getting full benefits from a nutritional shake just by taking it because you think you need to. They are best in the morning and after working out.