how long does "ready to use" formula last for?!

It should say in the container or box. If you've put it in a bottle and baby drank from it already then it's good for one hour.

doesn't it say on the back of the box the one I use does.

I don't have the box where the milk kame in I jus got 3 bottles from the hospital today I checked the bottles but it doesn't say

hope this helps i usually google