Baby feeding...help

Hi all....I just wanted to ask for some help/advice....my baby is almost 6 weeks young and he is bottle fed...he eats a mixture of formula and breastmilk (he didn’t like my boob from day one so I express)...now he is a big baba...at 4 weeks he weighed 11.2lbs and his height was 21.6inches (this is considered big where I am lol) anyway...He was eating 4oz every 3 hours and I have increased it to 5oz now that he is almost 6 weeks and he’s going through a growth spurt....he wants to only eat every 3 hours...how do I get him to eat every 4 hours during the day?