Path of the Magi, a third party book put out by Troll Lord Games featuring work by Sean K Reynolds among others, has a Histomorphy rules set that serves as an explanation for where owlbears and duckbunnies and other such creatures come from. They're covered from page 72 to 74 in my copy.
It uses a rather different creation time formula than magic item crafting, instead having a set period of time per the CR of the resultant creature but a monetary cost based on the HD it has and a flat XP cost.
It also has some skill challenges involved in making the creature and seeing if it is loyal to the creator or not.
Mostly a curiosity at this point, of course.
