Couldn't snap the bones in my chicken stock I followed Alton Brown's recipe for stock in which he gave a rough estimate of 8-9 hours at a low simmer to extract maximum flavor. At one point, he said, paraphrased, "How will you know you've extracted the maximum amount of nutrients from your bird? Well..." at which point he fetches a rather large leg bone from the discarded remains and easily snaps it in half. Alas I couldn't do that. I'm wondering if I did something wrong or if my results are typical.

I had a half carcass including wings, neck, back, gizzards, skin, and bones. They were raw and I froze them. For the stock, I gathered 3 carrots, 3 ribs celery half a bulb of garlic, and some thyme. I skipped on any salt or acids. I threw these with the frozen chicken into cold water, brought it up to a low simmer, and left it as such for 9 hours. The flavor was tremendous. Certain smaller bones became mushy toward the ends. However, I couldn't snap my bigger bones.
With all respect to Alton Brown, "snapping" the bones is not a test I have ever heard of.  He does not mention that in the official recipe on the Food Network site.

I just watched the entire episode on youtube, and he does show the snapping thing with a very frangible bone.   I think this result will depend on the age of your chicken and the size of the bone.

In general, the thinner bones and younger chickens may be somewhat rubbery when a chicken stock is done.

8-9 hours also seems excessive for poultry stock, although that is actually in his recipe.  You should get the vast majority of the flavor (and nutrition) in 3-4 hours (plus maybe a little bit to thaw, if you are starting from frozen), especially if you have chopped your carcass up into pieces or chunks (which he did not discuss in the episode).