Combine first 3 ingredients, stirring well. Unroll roast; trim fat. Reroll roast; secure at 1-inch intervals with twine. Cut 10 (1/2-inch-deep) slits in surface of roast; stuff thyme mixture into slits. Sprinkle with 3/4 teaspoon salt and pepper. Brush mustard over roast. Cover and chill 12 hours.
Preheat oven to 425°.
Arrange 3 rosemary sprigs crosswise on the rack of a broiler pan, and top with roast. Arrange 3 additional rosemary sprigs on top of roast. Bake at 425° for 50 minutes or until a thermometer registers 145° (medium-rare) or desired degree of doneness. Discard rosemary. Let roast stand 20 minutes before slicing.
Combine water and broth; add to broiler pan. Cook over medium heat; bring to a boil, scraping pan to loosen browned bits. Cook 4 minutes or until mixture measures 1/2 cup; stir in remaining 1/2 teaspoon salt. Slice roast; serve with sauce.