Sounds like a recipe for food poisoning to me. Formula or any kind of milk spoils and pretty quickly. I've come home after a 4 hour work shift to find a bottle DH had not picked up and the milk was already starting to curdle in it. IMO if it's been more than 2 hours since it was filled it's time for a good wash or a fresh bottle. 3 hours on the far outside. When my oldest was that age I'd go through 5-6 bottles a day.