I would not recommend to do that their tummies are still very small and it takes them one hour to process one ounce of milk now imagine throwing solids into the mix? Ur only going to harm your baby and give them problems of digestion. Ask ur doctor they will explain this to u.
I breastfeed, but when I have pumped and fed, my daughter has eaten 5 oz, but I have only done this once and she was going thru a growth spur and she was 4 weeks old, but now she's 5 almost 6 weeks old. You shouldn't really add cereal to their milk until at least closer to 3 or 4 months because their stomach is still maturing. My daughter during the day eats every 2-3 hours, depending on how growth. But at night she goes 6-7 hours.
Arya is 5 weeks tomorrow and is eating 4oz per bottle, shes only gone up to this much in the last few days. She goes around 4-5 hours between bottles. if hes eating more regularly than that, have you thought about the hungry baby formula, otherwise speak you your health visitor. xxx