1. Combine first 4 ingredients in a large bowl, stirring with a whisk until salt dissolves. Pour thyme mixture into a large zip-top plastic bag. Add pork to bag; seal. Marinate in refrigerator 24 hours, turning occasionally.
2. Preheat oven to 425°.
3. Remove pork from bag; discard marinade. Pat pork dry with a paper towel. Rub pork with pepper. Place pork on the rack of a roasting pan coated with cooking spray. Combine 1 tablespoon preserves and 1 teaspoon thyme in a small bowl. Place rack with pork in pan. Bake at 425° for 25 minutes. Reduce heat to 325° (do not remove pork from oven); bake 30 minutes. Brush preserves mixture over pork; bake an additional 5 minutes or until a thermometer registers 155° (slightly pink). Place pork on a platter; let stand 15 minutes before cutting into 1/2-inch slices.