I put out fresh feed every day, and the amount varies. If when I go down at night, the pan is empty, I will put out a little more the next day, if it still has quite a bit in it, I put out less. I do not really want feed available 24/7, as I think that draws in rodents.
In the summer, less feed, and in the winter more feed, in warm temperatures in the winter less feed, but if it sets in a really cold spell, more feed. Food will keep chickens warm.