There is no simple answer to his question as it does depend on what Fish you have, how big are they, how many Fish you have and what time of year it is. Fish are cold-blooded, so their metabolism is affected by the temperature of the water. The warmer the water the faster their metabolism is and the more they want to eat, the colder the water the less they will want to eat and in the coldest times of the year when water is low single digits or lower Fish will often cease eating altogether. But a simple rule to follow is to pop a small amount of food in, watch them feed, if they eat all the food then put some more in. Repeat this until they no longer show interest, any food left uneaten after a few minutes should be netted out otherwise it will decay in the pond and in large quantities can cause ammonia spikes.