Split hens down center. Place hens, skin side down, in two 13 x 9 x 2-inch baking dishes.
To make marinade, combine juice concentrate, lemon juice, chili sauce, Worcestershire and honey in bowl. Pour evenly over hens in baking dishes. Cover hens and refrigerate for up to 1 day, turning occasionally. (Can be frozen for up to 1 month; thaw in refrigerator before using).
Remove hens from refrigerator 1 hour before cooking. Turn hens in dishes; brush with marinade in dishes. Sprinkle on thyme.
Toss red and sweet potatoes, shallots, oil, thyme, 1 teaspoon coarse salt and pepper in bowl. Place in foil-lined roasting pan.
Heat oven to 400°F. Place potatoes on top rack in oven, hens in center of oven. Bake hens and potatoes for 40 minutes or until vegetables are fork-tender and meat is no longer pink near bone (185°F on instant-read meat thermometer). Stir potatoes and baste hens with marinade halfway through cooking. Transfer hens and potato mixture to platter; cover and keep warm.
Strain cooking juices from hens into 4-cup glass measure; defat (you should have 1 cup juices; add water or chicken broth to equal 2 cups). Place in saucepan with remaining 1/4 teaspoon salt. Bring to boiling. Stir in dissolved cornstarch mixture. Boil, stirring, until thickened, 1 minute.
Garnish hens with thyme, lemon and orange. Serve with sauce.