Well, the nice thing is that there are no hard and fast rules. You got options.
The pullets will start laying depending on breed and conditions- 16-30weeks or so.
The only real issue to worry about is feeding a layer type food too early is hard on kidneys. Layer feeds are supplemented with calcium for egg laying.
So you can:
Continue with the medicated starter feed till they start laying, then switch them over to layer feed.
Switch them to unmedicated starter feed till they start laying, then switch them to layer feed.
Switch them to a "flock raiser" type feed now, and supplement the calcium when they start laying, or switch them to a layer feed when they start laying.
"flock raiser" feed might be known by another name from different brands.
I think most people let the roos eat whatever the hens get. Kinda hard to stop them anyways.
Calcium is supplemented by feeding oyster shell, egg shell on the side. There are also lots of foods that are good sources of calcium.
1. Spinach & Swiss Chard
2. Salmon & Sardines (canned with bones)
3. Mustard, Collard, Kale & Turnip greens
4. Shellfish
5. Blackstrap molasses (can cause runny stools)
6. Corn Tortillas
7. Yogurt
8. Mozzarella & Cheddar cheese
9. Milk, Buttermilk (goat's milk and cow's milk)
10. Basil, thyme, dill seed, cinnamon, and peppermint leaves
11. Romaine lettuce
12. Rhubarb
13. Almonds, Peanuts & Brazil Nuts
14. Black Beans, Dried Beans (Cooked)
15. Sesame seeds
16. Fennel
17. Cabbage, Bok Choy, & Chinese cabbage
18. Summer squash
19. Green beans
20. Garlic
21. Tofu & Soybeans
22. Brussel sprouts & Broccoli
23. Oranges (Some people do not feed citrus to chickens)
24. Asparagus & Okra
25. Crimini mushrooms
26. Foods Fortified with Calcium: Some Orange Juice, Breads, & Cereals
Imp- hope this answers your question. I go the simple route- medicated starter till they start laying, then layer feed.