A pond that size (about the same size as mine) you do not have to feed the goldfish at all as there will be plenty of live food for them, plus algae, to eat. I feed mine once a day over summer though as it is fun and a good time to check all the fish are looking healthy with no obvious wounds or fungus on them, although there is plenty of live food zipping about in the water.
I also have to feed them before I mow the lawn or I get the giggles. As I move up and down the lawn beside the pond I find I have a large group of fish swimming beside me up and down as I go. It looks funny. :lol:
As the temperatures cool I feed less often, then not at all over winter. Once the temperature drops below 10C the fish semi-hibernate and stop eating so it is not good to feed them over winter if you live in a colder area. They can develop digestive problems eating in colder temperatures.