Remove baking dish from refrigerator and set aside. Let baking dish stand at room temperature, covered, 30 minutes.
Toward end of 30-minute window, preheat oven to 375º Fahrenheit. Uncover baking dish, then use spoon or spatula to scrape marinade off tops of chicken thighs and into dish. Be careful not to tear or remove skins of thighs.
Brush 1 tablespoon olive oil evenly across tops of chicken thighs. Season generously with salt to taste, then sprinkle ½ cup fresh cranberries and 4 sprigs fresh rosemary into marinade around chicken thighs in baking dish.
Place prepared baking dish in preheated oven. Bake chicken thighs, uncovered, 20 minutes. After 20 minutes, begin checking doneness of chicken thighs with internal meat thermometer. Continue baking chicken as needed, checking doneness every few minutes, until internal temperature of chicken thighs reaches 160° Fahrenheit.
Once chicken reaches 160° Fahrenheit internally, remove baking dish from oven and set aside. Preheat broiler to High. While broiler preheats, remove rosemary sprigs from baking dish and discard.
Brush 1 tablespoon maple syrup over tops of chicken thighs, then place baking dish under preheated broiler. Broil chicken thighs, watching closely, until skin on thighs is crispy and browned but not burnt. See Notes.
Once skins of chicken thighs have browned, carefully remove baking dish from oven. Immediately spoon cranberries and marinade from baking dish onto tops of chicken thighs, covering thighs completely. Let chicken thighs rest 3 to 5 minutes.