Rinse turkey inside and out with cold water; pat dry with paper towels.
Mix water, apple cider, kosher salt, and sugar in a large pot or 5-gallon food-grade bucket, stirring to dissolve salt and sugar. Submerge the turkey in the brine, cover the container, and place in refrigerator, 8 hours or overnight.
Preheat oven to 325 degrees F (165 degrees C).
Remove turkey from brine and discard used brine.
Place turkey with breast side up into a roasting pan; pat turkey and cavity dry with paper towels. Loosen turkey skin over the breast and thighs with your fingers.
Mix olive oil, thyme, and poultry seasoning in a small bowl. Rub the seasoned oil over the turkey and underneath the loosened skin. Cover turkey loosely with aluminum foil.
Roast in the preheated oven until an instant-read meat thermometer inserted into the thickest part of a thigh, not touching bone, reads 165 to 175 degrees F (75 to 80 degrees C), 4 to 4 1/2 hours.
Remove foil tent about 45 minutes before end of roasting time to let the skin brown.