Putting newborn formula in the fridge?

I have a newborn baby boy, he is almost 3 weeks old, my question is we feed him Enfamil milk (powder), so what I do is make 4 bottles (4 ounces) each and put them in the Fridge, when baby is ready to eat, I take one out and put in a bottle warmer, the rest stay in the fridge till baby ready to eat again, so a co-worker was telling today, we suppose to make the food on demand and not put them in the fridge