In an extreme case, such as the one that occurred in British Columbia, it can take up to 18 months because you can't put all the hens in the poultry barn at the same time. You can only produce at certain times during the year in order to supply the market. It takes six months from the egg stage before you end up with a laying hen. It takes 18 months for the process to start turning again.
On May 10th, 2007. See this statement in context.