Sprinkle 1 tablespoon of salt in the bottom of a dish or plastic container large enough to hold the duck pieces in a single layer. Evenly scatter half the garlic, shallots, and thyme in the container. Arrange the duck, skin-side up, over the salt mixture, then sprinkle with the remaining salt, garlic, shallots, and thyme and a little pepper. Cover and refrigerate for 12 hours.