Position a rack in the lower third of the oven and preheat to 450 degrees . Remove the giblets and neck from the turkey and reserve for making gravy, if desired. Rinse the bird and pat dry. Season the cavity with salt and pepper; place the lemon and rosemary inside. Tuck the wings under the body. Set the turkey on a rack, breast side up, in a large roasting pan. Rub with olive oil, sprinkle with the thyme and season with salt and pepper.
Transfer the turkey to the oven and lower the heat to 400 degrees . Roast, basting with the pan juices every half hour, until an instant-read thermometer inserted into the thickest part of the thigh, without touching the bone, registers 165 degrees , about 2-1/2 to 3-1/4 hours; cover with aluminum foil to prevent overbrowning, if necessary.
Let the turkey rest, loosely covered with foil, for at least 15 minutes before carving.