Feeding koi once per day could be considered "ideal" by any standard. Koi have ravenous appetites and it's uncommon to ever "fill them up" so people never get the sense that their fish are ":full". However, feeding carp (yes, Nishikigoi are carp) to satiety would require feeding them almost continually. This would destroy your pond water quality and mandate unreasonable water quality management efforts.

Feeding koi once or twice per day, all the koi fish want to eat in five minutes is the ideal to which most people should adhere. Breeders and growers usually feed considerably more food in order to push and sustain rapid growth. Again, this would destroy your water quality and mandate unreasonable water quality management efforts.

How MUCH should I feed my koi & pond fish?

When I was a kid I used to wonder how you'd "know" how much the fish would eat in five minutes. I wondered, "If I guess they'll eat a half cup and I am wrong, will I have to net out the uneaten food?"

So, all you do is start feeding, and keep a little food on the pond surface (with little spoonsful tossed often) for just five or so minutes. Make sure that you feed small pellets to small Koi and larger pellets if possible to larger Koi. However, if you are cohabiting large and small Koi, all the pellets will have to be small because the small Koi will always choose a larger pellet, even if it cannot fit it into it's mouth.