In medium non-reactive bowl, stir together cranberry juice, orange juice, soy sauce, oil, ginger and 1 tablespoon of thyme leaves. Set aside 2/3 cup of this mixture for use later in a sauce.
Pour remaining marinade in large zip-top bag and add flank steak. Seal bag and place in refrigerator for 2 hours to overnight, flipping bag occasionally.
Pour off marinade from steak and discard. Pat steak dry with paper towel and season with salt and pepper.
Add the 2/3 cup of reserved, unused marinade to a small saucepot along with fresh cranberries and bring to simmer, over medium low. Allow to simmer and reduce until volume of liquid halved and cranberries have “popped,” about 10 minutes. Use spoon to mash down cranberries, sprinkle in orange zest. Keep warm until flank steak done.
Spray grates of grill with cooking spray and bring to approximately 400 F degrees. Grill, covered, for approximately 16 to 20 minutes, flipping once. For medium rare, remove at 135°F or for medium, remove at 145°F.
Allow to rest on platter for 5 to 10 minutes. Cut against the grain (on “bias” or “perpendicular”) into thin slices.