I provide it when I start feeding anything other then their feed. So if they're only getting fed feed they don't need it.
I had mine on granite grit at that point, because I put then outside in a temporary "play pen" for a couple of hours each day when the weather was nice. They did pick and peck and even find a worm or two so I made sure they had it. It was suggested to me to take the regular grit and pound it in a towel with a hammer to bust it up into some smaller pieces, it worked well and they seemed happy to have it actually.
