How much to feed my baby. 1 month old

My baby is 1 mth old. Feed her 90ml - 100ml every 3hrs. No issues during night times. But during day time, she will sometimes cry for milk every 2hrs. At 2hrs, i will then feed her 60 - 70ml. In this case, can i feed her 90ml 3hrs later? My MIL advise me to feed her every 2hrs in the day and 3hrs at night. Not sure how can i drag from 2hrs in the day to 3hrs at night. Fellow mummies pls advise me am i feeding him right.. how do i know how much to feed my baby?