I would guess a 10lb turkey would still take over 3 hours to get to 165 at breast, although I am just going by the estimate of 20 to 25 minutes per pound at 275 that I saw online. I am not sure how accurate those estimates are though.
You've motivated me to try a spatchcocked one too in the Cookshack. Here is my plan below. The recipe is the YouTube video you sent plus a gravy recipe from Fine Cooking. I haven't tried any of this before so I am not recommending it. Even though I have a lot of directions below on the gravy, I will pretty much wing that as I don't know what to expect with the drippings. My main concern is to slowly add any smoked drippings while tasting to ensure I don't get too much smoke flavor since I never tried gravy before with cookshack drippings.
Smoked Spatchcocked Turkey on Cookshack
10 - 12 lb turkey that is already store-brined (such as Butterball turkey)
1 stick butter, softened at room temperature overnight
salt and coarse black pepper
2 medium to large yellow onions, unpeeled and cut into eighths
2 medium carrots, unpeeled and cut into 1-inch chunks
2 medium ribs celery, cut into 1-inch chunks
Cooking Wood:
1 chunk of pecan (3 ounces or less)
RICH TURKEY BROTH:
2 tsp vegetable oil
Giblets (liver discarded), neck, and backbone from the turkey (cut into 1-inch pieces)
1 medium yellow onion, coarsely chopped
PAN GRAVY:
Defatted drippings from drip pan below the turkey (add slowly and taste - don't add all at once to avoid a gravy that has too much smoke flavor)
2 Tbs Cognac
1/2 cup dry vermouth
2 1/2 cups Rich Turkey Broth
2 tsp lightly chopped fresh thyme leaves
1/2 cup heavy cream
1/4 cup all-purpose flour
Preheat the smoker to 275 degrees with 1 chunk of wood. Add the vegetables to a roasting pan and place below the rack that the turkey is on to collect the drippings for gravy.
Spatchcock the turkey (do not discard the back bone or giblets which will be used for gravy, although liver should be discarded).
With skin side down, drizzle olive oil all over the inside. Season with kosher salt and coarse black pepper.
Flip the turkey over and distribute the the stick of softened butter under the skin over breast and thigh meat.
Spread olive oil over the skin. Season the skin side with kosher salt and coarse black pepper.
Place turkey in the smoker. Insert temperature probe into the thickest part of the breast. Cook until breast meat is 165 degrees.
FOR RICH TURKEY BROTH:
Heat the oil in a 5 quart Dutch oven over medium-high heat. Add the giblets (don't use the liver), neck, back pieces, and onion; sauté until the giblets lose their raw color and the onion softens and begins to brown, about 5 minutes. Reduce the heat to low, cover and cook for 20 minutes; the turkey parts will release a lot of liquid. Add 1 qt. water, bring to a boil, partially cover the pan, reduce the heat to medium low or low, and simmer gently until the broth is flavorful, about another 30 minutes. Strain the broth into a fat separator or a 1-qt. heatproof measuring cup. Let sit until the fat rises to the surface and then pour off or skim the fat from the broth.
FOR PAN GRAVY:
1. Without scraping off any of the fond, strain pan drippings through a fine-mesh sieve; discard solids. Defat the drippings with a fat separator and set aside.
2. Set the roasting pan with the any remaining fond over two burners set on medium high. Add the Cognac, vermouth, and 1/2 cup of the rich turkey broth (not the smoked drippings but the broth made from the back bone); cook, stirring with a wooden spoon or wooden spatula to loosen the browned bits in the pan, until the liquid comes to a simmer. Strain the contents of the roasting pan through a large sieve and into a large saucepan. Add the remaining 2 cups turkey broth and the thyme to the saucepan.
3. Add a little of the reserved smoked drippings at a time while tasting to ensure you don’t get too strong of a smoked flavor in the gray.
4. Bring to a boil over medium-high heat; reduce the heat and let simmer to blend the flavors, about 5 minutes.
5. Meanwhile, put the cream in a small bowl and whisk the flour into the cream to make a smooth paste. Gradually whisk the cream mixture into the turkey broth mixture. Bring to a boil over medium-high heat, reduce the heat to low, and gently simmer to thicken the gravy and cook off the raw flour flavor, about 10 minutes. Keep hot until ready to serve.