The day before: score the skin of the duck breast to help render the fat. Either use a very sharp knife to score the skin in a criss cross, diagonal pattern, being careful to only cut the fat, not going into the duck meat at all. The second option for scoring duck breasts: use a sausage pricker. By gently pressing down all over the surface of the duck skin and fat, you're creating lots of tiny holes.
Dry out the skin. Once the skin is scored (or pricked), place duck breasts on a rimmed baking sheet and refrigerate uncovered for 8-12 hours, or up to 3 days. The cold air from the refrigerator will help to dry out the skin. This is key to getting crispy skin when you render the fat.
Preheat oven to 350F. Heat a small amount of canola oil (or other high smoke point oil, such as grapeseed or vegetable oil) in a large skillet over medium heat, no higher!
Cook the duck breasts. Season the duck on both sides with salt and pepper, then add skin side down. Cook undisturbed for 5-8 minutes, or until the fat has rendered. You'll know the duck is ready to flip when it easily pulls away from the pan, the fat has shrunk significantly, and the skin is crispy and golden brown.
Flip the duck. Gently turn the duck breasts over, being careful not to puncture the skin. (If you're adding any aromatics -- garlic, fresh herbs, etc -- this is the time to do so). Transfer the pan to a preheated oven and cook for 5-7 minutes (Pekin duck will only take an additional 3-5 minutes). Check temperature to ensure desired doneness is reached. For medium-rare, look for an internal temperature of 135 F.
Rest the duck. Allow the duck breasts to rest for 5-10 minutes before slicing into ¼ - ½" thick slices. Meanwhile, make the sauce.
Make the port cherry sauce. Sauté olive oil, garlic cloves, fresh thyme, and cherries in a sauce pan, about 1-2 minutes over medium-high heat, breaking up the jam with a spatula. Pour in port (or red wine) and chicken stock, then bring to a boil and reduce by half. Turn off the heat, add 1 Tbsp unsalted butter, then swirl the pan until butter gently melts. Serve over sliced duck with flake sea salt sprinkled on top.