How long is breastmilk mixed with rice cereal (refrigerated) good for?

We mix rice cereal into Rs bottles (on recommendation of his pediatric GI doc) to help with his spit up. I made a bottle yesterday for a sitter and he didn't touch it. I am finding conflicting info on how long it's good for? I have only a precious 2 bottles pumped so I really want to use it.

Thanks!