I've done turkey gravy ahead of time by making a good stock from turkey wings browned then braised with aromatics (celery, onions, carrots, bay leaf, peppercorns) and water for several hours and de-fatted. You can make an appropriate amount of roux (oil or butter plus flour) for the turkey stock, adding it and adjusting the seasoning, to get a good base for the turkey gravy. Then add drippings to boost the turkey flavor.