Girls, how much do babies on IV feed eat and at what time interval?

Girls, how much do babies on IV feed eat and at what time interval? My son is 3 months old and can't drink 180 ml immediately as written on the package, he drinks up to 90 max 120 (rarely). I give him 90 every time before each nap, sometimes 60 after an hour and a half, then 30 etc. Is this correct or should I keep feeding them 3 hours apart even if they ate little?