No worries that they will eat too much grit. They instinctively know how much they need.
Later when they get near to laying age you will want to provide oyster shell in another separate bowl. Only the laying hens need it or will eat it. By providing it separately you can feed an all-flock formula and not have to worry that any non-layers (males, old or young birds or moulting ones) may be getting too much calcium, which is not good for them, as may be the case if you offer a layer formula feed. Sorry about the run-on sentence.
Later when they get near to laying age you will want to provide oyster shell in another separate bowl. Only the laying hens need it or will eat it. By providing it separately you can feed an all-flock formula and not have to worry that any non-layers (males, old or young birds or moulting ones) may be getting too much calcium, which is not good for them, as may be the case if you offer a layer formula feed. Sorry about the run-on sentence.