it doesnt matter too much if you change too soon. detergents are detergents. they work right out of the bottle. they do not need time to start working. but if you change your oil sooner then you need to, all you are doing is spending more money (provided you are replacing the oil with the same kind). its like replacing your brake pads when there is still 15k miles left on the old ones. it doesnt hurt, its just unnecessary.