I never heard that Kirkland formula has to be made with "boiled" water! Does it say that on the container?
Gee.. that is the brand I used for my son... I just used regular bottled water. It was fine. I never warmed it up first. Just room temp. We've had no problems prepping it this way...
As far as how long you can keep prepared formula IF after they take a sip... well, I've kept it around, in the fridge for a few hours, or with my son who then would drink at-will as he needed. My son never had a problem. BUT, I never kept the bottle around for 24 hours if it was already touched. I ONLY kept an already UN-touched prepared bottle in the fridge for max 24 hours.
each baby is different about how they take formula....my son took it room temp or straight from the fridge cold. Some warm it slightly. But I never did this myself.
BUT, your son is only 1 month old... so, I would STRICTLY follow the care of the formula and keep it around for only as long as stated. My son, was on formula/cows milk AFTER 1 year old.
Yes, so after your son touches/drinks from his bottle...dump it out. Bacteria can grow in it or sour the formula. ONLY keep UNTOUCHED prepared formula... and yes, it can be kept in the fridge for up to 24 hours.
Your son is young... so do follow the storing 'rules.' That is safest.
Also, so as not to 'waste'... just prepare as much as you know your son can drink. If he then needs/wants more... then prepare more, a little at a time. At this age anyway... he probably drinks 3 ounces max? At then at night, for night feedings... I used to make some bottles ahead of time, untouched bottles, kept it in the fridge.. .and when or if my son needed a feeding for whatever reason, it was already made. OR, I'd keep it in a insulated bag/ice-chest next to my bedroom. For easy access and 'efficiency' at night when I was so tired.
All the best,