Fire up your grill for direct high heat cooking, targeting 400-450°F. Score the duck skin in a crosshatch pattern, cutting about 1/4 inch deep through the skin but not into the meat. This is crucial for proper fat rendering and preventing the skin from shrinking. Pat the duck breasts completely dry and season all sides with salt, pepper, garlic powder, and thyme. Let them sit at room temp for 15 minutes while your grill comes up to temperature.

Place duck breasts skin-side down on the hottest part of your grill grates. You should hear that satisfying sizzle immediately. Grill for 6-7 minutes without moving them - resist the urge to peek. You want that skin to get crispy and render out the fat. Flip the breasts and continue grilling for another 4-6 minutes until internal temp hits 135°F for perfect medium-rare. The skin should be golden brown and crispy.

While the duck finishes cooking, place a cast iron skillet on a cooler part of the grill and add the cherries, balsamic vinegar, and honey. Let this simmer and reduce for about 8-10 minutes, stirring occasionally. The cherries will break down and create a chunky sauce. Stir in butter and red pepper flakes if using. Taste and adjust sweetness or acidity as needed.

Remove duck breasts from the grill and let them rest on a cutting board for 5-7 minutes - this step is critical for juicy results. The internal temp will continue to rise slightly during the rest. Slice the duck diagonally against the grain into 1/4 inch thick slices. Fan out on plates and spoon the warm cherry sauce over the top. Serve immediately while the duck is still warm and that crispy skin is at its peak.