Feed them Grower until you start seeing eggs, then start providing extra calcium in the form of crushed oystershell or egg shells free choice on the side until you run out of Grower. Then switch to Layer.
Keep them on their starter until they are ready to lay. You will know they are getting ready to start laying when the combs, faces and wattles get really red. When the pullets start to squat for you, (they will hunker down when you lean over them) the eggs will be coming down the pipe soon! So that will be your que to go get some layer feed. Pick up some oyster shell too when you get the layer feed. Keep the oyster shell in a separate tub or feeder. They will eat it as needed.
Until then, enjoy your babies! I know the waiting for those first eggs is hard, but finding that first egg is THE most egg-citing thing!!
Good luck with your girls and welcome to our flock!