My son new born - 4 months, finished the milk sososososo fast, only take around 5 mins.....then 4-5months, take it slower......around 10mins, then change back to 5mins!!
Now he is around 1.5yrs, can finish 7oz milk around 5-10mins, depends on his apertize.
I think maybe adding other BB food such as cereal or juice affect the speed of drinking milk.