When it's done, take it off and let it rest before slicing. This recipe is perfect for those of us who are impatient -- the time it takes to cook the potatoes and the sauce is just the right amount of time the duck needs to rest. Don't skip ahead in the recipe -- follow it in order, and instead of trying to save time by slicing the duck while you wait for the potatoes to cook, do something else...have a glass of wine, clean up your previous course, etc. When we cook outdoors, I try to plan my meals so that while something is cooking (something that doesn't need my immediately and constant attention, like these potatoes), we can be eating a different course. If you use my beach picnic menu, start cooking the duck when you start eating your soup...that way, the multi-tasker inside you will be thrilled that you're eating, the duck is resting, and the potatoes are cooking, all at the same time.
I found some amazing maitake and chanterelle mushrooms while shopping for duck, so I added them to the pan right after cooking the potatoes and sauteed them briefly.