Go to All FLock/Flock Raiser and free choice oyster shell as soon as you are out of grower. Contra claims, above, Layer will **NOT** encourage them to lay. Its only value is that its cheap.
The higher protein content of All Flock/Flock Raiser will benefit your birds in (slight, but measurable, though not visible) increases in rate of lay, size of eggs, content of eggs. It will additionally help with weight gain and feather condition, helping to speed molting when your birds do their first adult feather replacement.
Due to larger bag size, you will find the All Flock cheaper per pound than your current feed (though admitedly, not as cheap as layer).
Later, if you should add more birds to your flock, either as hatchlings, roosters, or other hens, there will be no need to either switch feeds or structure seperate feeding areas. All your birds can eat All FLock/Flock raiser (assuming its crumble, wet mash, or fermented) all of their lives.