Heat oven to 350° F. Heat 2 tablespoons of the oil in a large ovenproof skillet over medium-high heat. Add the plums, thyme leaves, 1/2 teaspoon of the salt, and 1/4 teaspoon of the pepper. Cook, stirring occasionally, until the plums soften and release their juices, about 3 minutes. Transfer to a bowl. Return skillet to medium heat and add the remaining oil. Season the pork chops with the remaining salt and pepper. Cook until browned on 1 side, about 5 minutes. Turn, top each chop with 1 thyme sprig, and cook for 5 minutes more. Spoon the plums around the chops and transfer skillet to oven. Roast until the pork is cooked through, about 5 minutes. Divide the chops and plums among individual plates.