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However depending upon where you are the winter cold and shorter daylight hours will play into how soon they will lay.
I try to get my pullets to 20 weeks by July or August latest so they get established in laying before the onset of winter hours otherwise they don't seem to kick in well until spring especially if one of their last juvenile molts occurs at the normal fall molt time.
Hopefully yours won't mind the winter and will set in to laying well soon. Adding lighting to the coop can help to extend the light time to beyond 12 hours each day. (Just don't leave it on all the time or you can cause some egg laying issues and chicken irritability. Also be careful with any lighting...I've burned a coop down and so have several of my friends.)
Lady of McCamley
I agree with the others-- white Rock hen coming up on point of lay.
Just a correction to Lady, above--they need a minimum of 14 hours of light to affect egg production. 12 hours will just waste electricity.
If you add light, be sure to do it gradually, like 10-15 minutes more light every 3-4 days until you're up over 14 hours of light a day. Jumping from 10 hours of light (what we have naturally this time of year) to 14+ won't do you much good.
Here is a great link to a University website: http://umaine.edu/publications/2227e/