Hello Ella and welcome to BYC, You found an Awesome poultry Forum to be a part of with many great knowledgeable members who are more then willing to jump in and help you with any questions you may have.
Hi Ellen, welcome to BYC!
(I have a beautiful black langshan pullet named Ella.)
You can introduce chick grit at any time. They will eat it if they want it, although, as long as they are only eating chick feed, they don't have to have it.
I usually give my chicks a cat litter pan full of dirt from the run while they are still in the brooder. They live to dust bathe.
Good luck and congratulations on your new chicks!