Why does powder formula go bad after an hour?

Bacteria, formula when dry is too dry for bacterial growth - this is why jam works since sugar in jam is hydrophilic (water loving) and takes up the water which discourages bacterial growth, same with salt on salted foods like salted fish or heck, jerky.

When you add water to dry formula you have made a bacterial medium, a broth that is nutrient rich to bacteria and this encourages growth - the same way that food that is heated above 41F and below 150F does as well (warm foods that should cold at picnics make people ill too). But with breastmilk it isn't a bacterial media as it wasn't sterilized, it is full of antibodies and white blood cells from mom that actively attack bacteria allowing it to sit at room temp for up to 10 hours.

I really do not know the answer to your question, I never had children so I have never boughten formula. I seen mothers caring around bottles all day but as to if it's breast milk or formual I have no idea. Sorry I can't help you out more.

If you leave it out, yes. But if you put it in the fridge it's good for 24 hours.