Well, it seems to me that bees' brood cycle is somewhat like a human life cycle. Conception can occur at any time, but there is a relatively fixed timeline for the various development stages and birth of the fetus.
It works that way for bees also, as you can see from Michael Bush's BeeMath page:

http://www.bushfarms.com/beesmath.htm
It works that way for bees also, as you can see from Michael Bush's BeeMath page:

http://www.bushfarms.com/beesmath.htm