Mixing breast milk and formula and storing in the fridge

My milk supply has been dramatically decreasing and my baby has a dairy intolerance. So I have been trying to supplement formula while I try and get my milk supply back up. She hates the formula so much and it smells awful even when combined but currently I mix a quarter of what she is eating with formula and the rest breast milk to try and get her used to it. Usually I just put the bottle together right before she eats but I currently have a bottle in the fridge I mixed together tonight to be able to use for the morning. Because it will be sitting in the fridge for 8 hours is this ok? I know the formula can sit in the fridge for 24 hours once it’s prepared. I am just not sure if the formula will cause any type of issues to the breast milk for them to be sitting there combined for so long.