Cut slits on the top of pork loin, about 1 inch deep. Plug in apple slices into the slits. Set aside. Add slices of butter, onions and remaining apples in the slow cooker. Add pork loin. Sprinkle pork loin with salt, pepper, and cinnamon. Add the thyme. Drizzle over the honey. Cover and cook on low for 6 hours without opening the lid during cooking time. When finished, remove pork to a platter and let rest for at least 5 minutes. Slice and serve.