If it says "layer" on the bag, it is lower protein than chick feed or starter, and It Has Extra Calcium. I (or the co-op guy) accidentally killed about 50 birds @12 weeks old by feeding them laying mash/crumbles. Within two months they were dropping dead left and right, Kidney failure...
You shouldn't put them on layer pellets or mash until they actually start laying. The difference between layer and regular feed is layer had more calcium, that's about it. It doesn't magically make a pullet lay. layer feed only provides the extra calcium needed for strong thick shelled eggs...