1. Preheat the oven to 325 degrees F (165 degrees C).
2. Rub the pork with the thyme and mustard powder to your liking. Put into a dish that is nonreactive and add 1/2 c of the soy sauce, 1/2 c of the sherry, garlic and ginger. Cover the loin completely. Cover and keep refrigerated overnight.
3. Bake this at 325 degrees F (165 degrees C) until internal temperature reaches 160 degrees F (70 degrees C) or for approximately 25 minutes per pound. Continue to baste the pork while cooking.
4. While this is baking, heat the apple jelly in a small saucepan over medium heat. Add 1-tablespoon soy sauce and 2 tablespoons sherry. Mix this thoroughly. Reduce the heat to low and let it simmer. Pour the sauce over the tenderloin when it has heated through.