That depends on several factors. What brand and type of feed is your chick feed and "regular" feed? Do you have older hens in your flock?
I use Purina Mills' Chick Starter as long as I have babies. According to their site, you can start using All Flock as long as everyone is over 7 weeks old, but you'll want to have free-choice egg shell or crushed oyster available for any laying hens. You do not want to use Layer feed until your girls are actually laying because the excess calcium in it can damagee their livers. That is why many old timers recommend avoiding the layer blend and stick to offering fred-choice calcium.
It also depends on your breeds. Bantams and Silkies, for instance, eat less than Barred Rocks and Marans. And free-ranging changes the amount of feed, too. A flock in a lush, green pasture with lots of bugs will eat less feed than ones in an average backyard.
Personally, I'd recommend using their age to reach the seven week mark and switching to an All Flock type feed. Just ensure there is free-choice calcium available by week sixteen. That is generally the earliest most breeds seem to start laying. They won't eat it until they need it.