Bake 2 to 2-1/2 hours or until 130°F to 135°F for medium-rare doneness. Remove from oven. Cover with foil; let stand 15 to 20 min. before slicing. Meanwhile, mix 1 cup Miracle Whip
and horseradish in small bowl. Mix remaining Miracle Whip
, Sweet Onion Dressing and thyme in separate bowl.