The final look is pretty much obvious at the 8 week mark. Whatever changes remain due to outstanding swelling will be minor.
I'm not sure you can extrapolate from your single jaw surgery results to make a claim about double jaw surgery. Even though I'm inclined to agree with you I think there's some pretty resistant swelling that warps results. I'd say 90 percent of cosmetic improvement is there at 3 months.
However, for nerve regeneration I'd say a year. And I say that because I was in some crazy fights where my face was hit and the nerves didn't get back to 100 percent till a year's end. And that was just a blow. Now think of the trauma of double jaw surgery where your bones and flesh is cut up on a butcher's block and stretched around. That should at least take a year.