My extra roosters and tom turkeys are my main meat source. I have Royal Palm turkeys which are a heritage breed smaller than commercial turkeys. Keep in mind that, "opinions vary", but here's how I do it, and maybe more than you were asking--
First, I can't think of any reason why a heritage breed turkey would cook sooner than a commercial turkey. The length of time needed would relate to the size/poundage of the bird, and also how old it is, as a young confinement-raised commercial turkey would be more tender to start off than a 2 year old pastured heritage breed tom. With that said, the older heritage breed tom (or chicken rooster) can be cooked just as delectably tender as the storebought, and everyone who has tasted one of mine agrees that they are more flavorful. You want them to be eating grain based food (normal poultry feed) for several weeks before slaughter rather than scrounging wild greens and berries and who knows what, because "you are what you eat", and like the cow eating wild onions will have onion flavored milk, the turkey eating young pine twigs etc. will not taste so good.
Here is a CRITICAL STEP to having a tender bird instead of a tough one, and it doesn't matter how old the bird is--whether you butcher it or have it done, do NOT immediately freeze it. Just like prime beef has to age in the meat locker to become tender, a chicken needs to wait 3 days in the fridge and a turkey needs to wait 4-5 days in the fridge depending on size, at just above freezing (like 34-36 F) to age and tenderize. If you or the processor puts the carcass directly into the freezer you have just about guaranteed yourself a tough meal. Most processors are good with this as long as you are picking up your birds the day of slaughter; it's not fair to expect them to hold your birds in their limited fridge space for a week or more until you can get around to picking them up.
Incidentally, I don't soak my birds in water "to get the blood out" as I've read some people recommending. It seems like a good way to invite bacteria to grow to me; I don't know? I've never noticed any more blood in a carcass than in storebought poultry. I kill them, clean them, rinse them thoroughly in running chlorinated tap water, put them in a plastic bag and stuff them in the fridge directly for aging, then into the freezer.
As to cooking, you want to use a tight covered pan up until browning at the end, and if your pan lid doesn't seal tight enough to keep moisture from evaporating during cooking, seal first with aluminum foil then put on lid. LOW heat over a LONG time will give you a moist tender bird ready to fall off the bones, and a wonderful stock in the bottom of the pan for gravy, flavoring stuffing, soup base, ???. Pasture raised poultry will always have more "chew" than grocery store birds, which are 1-still infants, and 2-usually pressure treated with a water solution to raise the weight. This is what most people have gotten used to, but to me it's mushy and tasteless. Pasture raised poultry is more like cooking and eating pheasant.
I put the bird in the fridge for one or more days so it's thawed before cooking. I cook my birds in an old/antique heavy aluminum Guardian roaster with a tight glass lid, or a larger enameled metal roaster with lid; my oven is only set at 175 F, and I put them in the oven in the evening and take them out when I get up in the morning. You don't have to take that long, you could cook at 200 and start in the morning to have it ready for supper (about 6 hours), but slow, low temperature cooking is the key to a moist and tender bird. For food safety, you have to keep your meat at above 145 F while cooking.
I usually sprinkle on some herbs/poultry seasoning, but don't salt until after cooking. If I'm using the enamel roaster I add water in the bottom because that lid isn't as tight, then put turkey on a rack. I don't stuff birds, but wait and make the stuffing flavored with juices from the bottom of the pan. To finish cooking a bird, I take the lid off, rub the skin all over with a stick of butter, and raise the oven temp to 300-350 F and keep an eye on it until it's browned. Then remove, LET IT REST for at least 20 minutes before cutting. As with a beef roast, this step is important to keep from losing the meat juices when you carve the bird.
I think you can also find cooking information for heritage meats on the Slow Food Ark of Taste website. May your tastebuds celebrate!