My flock free ranges from dawn to dusk daily and has free access to feed 24/7. My husband and I built large wooden gravity bin type feeders, two of which that hold 50 lbs and one that holds well over 100 pounds of feed (stays dry and free of pest thus far). I have three coops and each has its own feeder. I will fill it and then watch the tray...if the feed looks thin, I will push the food toward the middle on the inside and if it starts getting low I top it off. Typically, in one month my birds (70 total counting the guineas and chickens) will consume between 250 to 300 pounds of feed, which breaks down to a little less than 1/7th cup on the high side to 1/9th cup on the low side per bird per day. Going by the 1/4 cup/bird/day figure that is the standard measure for an average chicken....I should be feeding a total of 525 lbs of feed a month. So, I would say that they only eat when they are still hungary and no more.
Oh and as another poster noted about lower ranking hens.....I have a couple small, low ranking hens that I am sure would starve if I restricted the food to morning and night feedings. They run to the feeder every morning when I let everyone else go outside to range. Then, in the afternoon when most everybody comes in for a siesta, the lower ladies scoot outside to forage. Considering the recommendation is for 4 inches of lineal feeding space per bird...I would need a feeder that was a bit over 23 feet long to ensure everyone had room to eat with restrictive feedings. Yikes...that would be quite a feeder.