1. Preheat oven to 350°F. Combine maple syrup, thyme and garlic in medium bowl. Reserve 1/4 cup for squash. Brush half of remaining syrup mixture onto all surfaces of beef roast. Reserve remaining for basting.
2. Place roast, fat-side up, in shallow roasting pan. Insert ovenproof meat thermometer so tip is centered in thickest part of beef, not resting in fat or touching bone. Do not add water or cover. Roast in 350°F oven 2-1/4 to 2-1/2 hours for medium rare; 2-3/4 to 3 hours for medium doneness, basting with syrup mixture halfway through roasting time.
3. Meanwhile, place squash, cut sides up, in 13x9-inch glass baking dish. Brush cut sides of squash with some reserved syrup mixture; evenly pour remaining mixture into each well. Roast, uncovered, 45 minutes, brushing cut sides with syrup mixture from wells, halfway through baking time.
4. Remove roast when meat thermometer registers 135°F for medium rare; 150°F for medium doneness. Transfer roast to carving board; tent loosely with aluminum foil. Let stand 15 to 20 minutes. (Temperature will continue to rise about 10°F to reach 145°F for medium rare; 160°F for medium.) Meanwhile, increase oven temperature to 425°F and continue to roast squash 15 to 20 minutes or until tender and edges begin to brown.
5. Carve roast into slices. Cut each squash in half, then into 2 wedges. Carefully spooning syrup mixture onto each wedge. Season beef and squash with salt and pepper, as desired.