You can start any time you like, but yes, you MUST give them grit if you're giving them anything but basic chick starter. IME, if you make them a nice dust bath area they can play and scratch around in and put the grit in there, you will have happy, entertained chicks. I used a rubber tub from Tractor Supply.
Okay thanks! Do I just buy a baby chick grit? Is there such a thing? I have them inside the house in a kids connecting panel gate. I use thick paper towels as the floor cover, but I do have an old tin in there full of pine shavings and food so they can scratch if they'd like. Should I be putting dirt in it instead? I didn't figure they'd need it bc they're not outside.
Yes, you buy chick grit. Any farm supply will have it. Dirt is up to you. Dust bathing is a natural activity and mine would go absolutely crazy every week when I refreshed their dust bath.