Rub roast all over with garlic, onion powder, and 1½ teaspoons thyme. Sprinkle with salt and pepper. Place in a shallow roasting pan and roast for 1 hour.
Meanwhile, peel and quarter potatoes or cut into wedges. Cook potatoes in boiling water for about 10 minutes. Drain and let cool slightly. In a large bowl, toss potatoes with olive oil, remaining thyme, chives, and garlic powder; sprinkle with salt and pepper.
Arrange potatoes around roast and return to the oven. Roast for about 1 hour longer or until pork registers 155°F–160°F. Remove from oven and loosely cover with foil. Let rest for 15 minutes before slicing.
Slice and arrange on a serving platter with potatoes.