That would be fine, but I wouldn't introduce any other new food items for a week or two. Like the above poster said, it would be best to give it to him by itself for the first couple days, then you can mix stuff. You can give the cereals anytime of day that you would prefer.
It's fine as long as he doesn't have any kind of reaction to the oatmeal. Give it to him by itself a couple times first.
I personally see nothing wrong with giving him one in the morning and one at night, and yes you can still mix fruit with the oatmeal.