No, using formula milk that has been produced and kept out at room temperature for longer than two hours is generally not advised. Bacteria can grow quickly in formula milk at room temperature. If the formula is prepared and not used within one to two hours, it should be stored in the refrigerator immediately. Refrigerated formula should be used within 24 hours. It is best to throw out the formula if it has been out for longer than two hours in order to reduce the possibility of foodborne disease.