When will they lay?

The wait is always hard! There are so many factors that it is hard to give an acurrate date. Even within the same breed the type of breeder can make a difference. Hatchery birds tend to start a little earlier and breeder birds a little later. For the average bird of common breeds, like your birds, 24 weeks is generally considered a good average from most sources.

In my experience anywhere from 4-8 months is still in the normal range so if you pass 24 weeks don't panic yet. Watch for their combs and wattles to turn a nice bright red and for them to start squatting when you approach. They might also start checking on the nesting boxes. All of these behaviors indicate they are almost there.