Whisk garlic, chiles, ginger, oil, soy sauce, vinegar, sugar, fish sauce, and salt in a medium bowl until sugar and salt dissolve. Add lemon slices and thyme. Place marinade and chicken in a large resealable plastic bag. Turn to coat, and chill at least 12 hours.
Heat oven to 450°. Remove chicken from marinade, shaking off excess, and place, skin side up, on a rimmed baking sheet. Roast until cooked through and an instant-read thermometer inserted in the thickest part of the thigh registers 165°, 25–30 minutes. Serve chicken with lemon wedges for squeezing over.