Place pork in a shallow dish and season with salt and pepper.
Combine garlic, thyme, balsamic, mustards and olive oil in a small bowl. Season with salt and pepper. Pour half over pork. Rub glaze over pork and let sit at room temperature for 30 minutes.
Transfer pork to a roasting pan fitted with a rack and pour 1-½ cups (355ml) water into bottom of pan. Roast until internal temperature reaches 140F (60C), about 1 hour, basting with reserved glaze every 10 minutes after first 30 minutes of cooking. Add more water if pan becomes dry.
Transfer to a cutting board, cover with aluminum foil and rest for 10 minutes before slicing to serve.