How many chicks? Do you have any older birds? You can keep them on unmedicated starter crumble, or switch them to a grower which is at least 18%, or put them on a multi flock feed which is 18 - 22% protein, and keep them on that until they start laying. Your choice whether you then put them on layer, or keep them on one of the other feeds. Grower here is only 15%, so I never buy it, and I am comfortable putting my youngsters on layer any time after the pullets get their cluck (meaning they no longer peep like babies, but cluck like hens. They are still youngsters, but they are going through chickie puberty).
IMO, the most important thing is to see to it that their feed is not stale. 6 weeks after feed is milled, the nutrients start to break down. I try to finish up a bag of feed before it is 6 weeks old. Always check the mill date on the sew tape on the bottom of the bag before buying the feed.