opened oatmeal

How Long Can Cooked Oatmeal Last In Fridge? Properly stored, cooked oatmeal will last for 4 to 6 days in the refrigerator. How long can cooked oatmeal be left at room temperature? Bacteria grow rapidly at temperatures between 40°F and 140° F; oatmeal should be discarded if left out for more than 2 hours at