OK. A couple of points here.
Chickens don't all start laying at the same time, even if they are the same breed. It depends on many factors including just individual physical variation.
I *really* recommend you stop the layer feed for multiple reasons.
#1- Most layer feeds are lower in protein (16%) and younger birds need higher protein to develop properly.
#2- Layer feed has about 4x more calcium than is recommended for non-layers (young pullets, older hens, cockerels, when they stop laying in winter, etc.). It is not healthy in the long run for non-layers and can lead to serious joint pain, which I'm sure you don't want.
In fact, there are so many exceptions to when it is okay to use layer feed, that I finally stopped and switched to flock feed (18%+ protein) + oyster shell full time. No more switching feed types. Everyone can eat the flock feed and the layers can still get their calcium. The only issue is that very young birds need crumbles instead of full-sized pellets, but that is easily available.
I recommend you switch to flock feed ASAP, seal up the layer feed and use it up when they are all laying. One note on switching feeds. Chickens don't like change once they've found a routine, including food. When you want to switch feeds, mix some of the new in with the old so they can adjust to the new taste. Take a few days to a week to transition.
