They can eat as much as your filter can handle. If I sit by my pond for two hours, I can toss small amount of food for the entire time and the koi do not get tired of eating. In the wild, carp browse constantly for food, eating almost non-stop. They have no stomachs, only intestines. So if the food is of a high quality (no corn which is very high in carbohydrates, leading to obese fish), feed them as much as your filter can handle.

However....the biggest drawback you have is the size of the pond they are in. A koi should have a minimum of 250 to 300 gallons each (minimum pond size for koi is 1000 gallons), and a goldfish should have 50 gallons each. So at that rate, you are already way overstocked. Your filter probably cannot handle frequent feedings.

Here's another draw back to feeding them every two hours. The more you feed a koi, the bigger they get.

"It seems the fish will eat every two hours or so if fed"

So will I, my wife says!!!