How long does a formula bottle last once made up?

24 hours
If made-up formula is stored: in a fridge – use within 24 hours. in a cool bag with an ice pack – use within 4 hours. at room temperature – use within 2 hours.

Why can’t you use formula after an hour?

After you prepare formula, any formula that is left over in the bottle your baby drank from needs to be thrown away. This is because that bottle now has bacteria from your baby’s mouth in it, which means it might be contaminated with germs.