I wait until 7-10 days. I feed chopped cooked egg, snipped grass or clover, cracker or bread crumbs. I also add grit at this time. I mix it with their chick starter - 10% grit.
If you give them anything besides Starter feed be sure to give them some Chick Grit. Chick grit is finely crushed granite grit. I smash some of my regular grit or you can buy it. My Tractor Supply store carries Chick Grit.