Hi,
My opinion is this; IF THEY EAT, YOU FEED. Do not leave any uneaten food floating in the pond after 15 minutes. Koi will eat less as the water temperature goes down. (It takes five hours for a Koi to digest food at 20*C)
If the water temperature is less then 10*C, Koi will not eat!
I feel that one should not feed Koi for a period of 30 days during winter; it will help the Koi to use up excess reserves, i.e. unused eggs, and get into condition for the following season, making the chances of female Koi becoming egg-bound less likely.
I normally stop feeding during July, and slowly start to feed during August with normal feeding in September.