It should really be daily if they're eating anything besides their crumbles/pellets, but if that's what you've been doing, it's obviously fine or you'd have had some digestion issues by now.That is really good to know. I let my chickens free range a few times a week. Is that enough for the grits?
If you have a garden and are where the ground isn't frozen yet, and the dirt is course/grainy and not like silt, you could fill a jumbo kitty litter box with it, a sprinkle of wood ash, diatomaceous earth, or 1st Sat Lime (for mites) and put that in the coop. Then they get their dust bath and grit all in one. Ours free range, but once the snow covers the ground, they're just pecking snow after that, so that's how we take care of two issues in one.
Hiya, and welcome to BYC!!

which I eat quite regularly. You did get good advice on keeping some free-choice. My chickens free range, and there are sufficient grit pieces in the soil they scratch in.
I didn't know I was getting ducks. My husband comes home one day, and there are these cute little yellow balls of fluff. What to do? Keep it! That started the chain of two-legged feather friends; next thing I know, I'm surrounded. We still have to make room for everyone, but this spring we will ensure everyone has room. I feel horrible about not being knowledgeable about what they need, and I really appreciate all of your advice. Thank you, thank you