I feed once daily, in the evenings (to ensure they sleep with full crops, give me a chance to monitor flock health, some impression of how well they are foraging, get them back into the runs, etc) and force the birds to forage all day. It works for me and my flock. I didn't read it anywhere, its not backed by any studies I'm aware of, and is just sort of something that "happened". So my example should be considered anecdote, not data.
During the day, its not uncommon to see the chickens hiding in the shade, dust bathing, doing everything BUT foraging for a while. Then off they go to forage some more... I don't pretend to understand it, can offer no reason for it - but every bird I butcher for the table seems healthy, and I can't complain about the quality of the eggs - so I let my chickens be chickens. They are better at it than I am.