I have a different approach to this.
My chickens have constant access to both a balanced layer ration and unlimited veg/greens. I allow them to choose what they eat and when. I find they tend to eat their layer ration for breakfast, then after a big drink of water they come out of the coop and graze on broad-leaf weeds and grasses in the lawn. Then they stop for a rest and preen their feathers for a while.
After that they spend most of the day scratching around in the garden beds, eating bugs and nibbling at whatever fruit, veg, nuts and seeds they choose from the garden. They also pop in and out of their coop during the day for another few pecks of food from their hopper, and take drinks from various containers (and puddles!)
Mid-afternoon they take another rest from foraging, and this is when they dust-bathe if it's a sunny day. This is also when they hop up on the decking rail and look in the window to see what I'm doing.
Just before bed they top up with some more food from the hopper in their coop.
Research on 'pastured poultry' (i.e. hens with unlimited access to both plant material and pelletted feed) shows that they will choose up to 30% of their calories each day from vegetable matter. 30% of their calories means considerably more by weight. I'm always amazed how much grass mine eat.
A sudden change in diet can definitely have side-effects like runny poo. And if your birds are penned, they are likely to gorge themselves on whatever you put in there because it's new and interesting. But if they have constant access to veg, all day every day, they will eat just as much as they need.
