Hello Jason, thankyou for your question.
Oatmeal can be kept up to one week in refrigerator.
Oatmeal is fine to keep covered and in the refrigerator though it tends to stick together.
When reheating do so with a little milk well mixed first and heat only till ready to eat.
This will not be the same texture as when originally cooked but is edible.
If you have any more questions please let me know. Otherwise just click "Accept" and leave a positive feedback as I will for you also.