To prepare duck breasts in advance, score the skin, season them, render off the fat and sear them ahead of time. Then place covered in an oven-safe dish (in room temperature if just for a few hours, otherwise in the fridge). 20 minutes before you want to eat, place the duck in a preheated oven with an oven thermometer and cook to your set point - and don't forget to let the duck breasts rest at least 5 minutes. For this specific recipe, I recommend making the orange sauce in advance as well, and heating it up just before serving.