Since I am in Maintenance, I tried eating them... they awakened the carb-addicted monster in me as much as a piece of cake would have. I've tried on more than one occasion, and, no way. It would be nice to be able to fall back on one in an emergency, but alas, they are not for me.
In answer to your question as to when to have them if you are one of the ones who can tolerate them - look on the ingredients list of the one you want to try. Amongst the zillion chemicals that are listed, try to find some that you recognize... whatever the highest rung is to those, is where you add it. For example, there's usually soy in them. That means no-go until at least Rung 6. It there are any kind of oats in them, that would be Rung 9.
As I indicated, I waited until Maintenace, and they still did a number on me. The ingredients will determine when you add it, and it's one of those YMMV (Your Mileage May Vary) things as far as tolerance.