Pre-heat the water bath to 131°F (55°C). Cover the prime rib roast with salt, pepper, the garlic, and ancho chile powders and place in a pouch. Add the thyme and rosemary to the sous vide pouch and then seal the roast. At this point you can store the pouch in the refrigerator for up to 2 days, freeze it for up to 6 months, or cook it right away.
At least 6 to 11 hours before serving
Place the prime rib roast in the water bath and cook for 5 to 10 hours depending on the tenderness of the prime rib roast you are using. For a grass-fed sirloin roast 5 hours should be good up to 10 hours for a supermarket prime rib.
For more information on the cooking times you can read my detailed article which addresses why is there a range in sous vide cooking times.
Preheat the oven to 400°F (200°C).
About 40 minutes before the sous vide prime rib is done you will want to roast the garlic. Take the peeled garlic cloves and place them on a square of tinfoil. Add the rosemary and thyme leaves and the olive oil. Fold the tin foil around the garlic to make a sealed pouch and place in the oven.
After about 30 minutes check the garlic to see if it is tender. It will likely need another 10-15 minutes but you want to make sure it doesn't burn.
Once the roasted garlic is soft mashed it with a fork into a paste and set it aside.
Preheat the oven to 450°F (230°C)
Take the sous vide prime rib roast out and the water bath and remove it from the pouch. Dry it off with a paper towel or dish cloth and place in a roasting pan. Smear the paste on the sides and top of the sous vide prime rib. Place the roast in the oven until the crust is done, about 5 minutes.
Remove the sous vide roast from the oven, slice it into strips and serve. It is great served with mashed potatoes, a side salad, or mixed vegetables.