Ive got a 12 week old baby who weighs 14 pounds, he is taking between 6 and 7 ozs five times a day, 4.30am, 10am, 2.30 pm, 6.30pm and 11.30pm. he is currently on aptamil first milk would i be able to swop his last feed at 11.30 to hungry milk to get him sleeping a little bit longer or do you have to stay on just one type of milk??