I was always told not to make up the formula in advance so I always made it fresh. I had a formula measuring container and would have the formula already measured out so that all I had to do was grab a bottle of water (I would fill the bottles with cooled boiled water and seal and set aside to use when needed (this was better than refrigerating because otherwise I would have to heat it from cold).

I honestly think its alot easier this way than having cold formula that takes longer to reheat.