I actually just leave a huge chunk attached to the side and they chomp on it when they want. I'd just put in another chunk when you see that the first one is gone.
I give my two girls cuttlebone just about everyday....sometimes they eat it all right away, sometimes they ignore it. Remember to remove the brittle backing.
"Make it turtle proof, and they'll build a better turtle."
Most cuttlebone has one side that has a hard backing, although a few people have said they've been able to buy pieces without it. If both sides of the cuttlebone you buy are like chalk and you can easily dig your fingernail into them, then you don't have to worry about the backing.
"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-