If you get them earlier, you can just butcher when they reach the size you want and put them in the freezer until Thanksgiving. I raised heritage last year (poults I hatched from my own eggs!) And the toms we butchered the week before Thanksgiving were over 20 pounds dressed. They hatched at the beginning of May.you do understand how big they will be and how much feed they will require by thanksgiving if you start them in the spring, right??? I recommend bronze vs white if starting earlier
Heritage will take longer to fill out, but usually don't have the mobility issues of the broad breasted. In my experience the heritage usually have more leg meat and broad breasted have more breast meat.