They know when to quit. If you are trying to monitor how much they eat chances are they are so hungry when you go to feed again, they're gorging themselves. They are going through an incredibly fast growth period and need the food to be there.
Chickens are better than humans at knowing how much and when to eat.
I always tell folks to feed their chicks what they can clean up in a meal and give them a couple of hours. Then do it again that evening. If they are licking the plate, add a little more. If they leave some behind, feed a little less.
Chicks raised by a mama do not have constant access to food, so yours don't need constant access to food either. Chickens always act like they are starved, no matter how much they are fed...that doesn't go away. You can watch them eat until their crops bulge and then get out some grains and throw them on the ground and they will all run to eat them like it was the first meal they have had in a week.
At 2 wks mine get turned out on range to find their own grub all day and are fed once in the evening with all the big birds. If you are not free ranging, you can stick with the twice a day feedings until they fledge out and then just do one meal.
I never feed free choice feeds...the rodents will soon learn where the buffet is and you start losing food and attracting vermin. If they are confined to a pen/run they don't need constant access to food as they are doing no exercise at all but walking around in a little space. If free ranging, they get both exercise and free nutrition out on the grass, so feeding once a day works for that as well.