In a large bowl (or 2 freezer bags) add the chicken with 1 quart buttermilk. Refrigerate overnight. When ready to fry, remove chicken from bowl and let sit on counter for 30 minutes to take chill off.
Preheat oven to 350F. Stir together the flour, seasoned salt, pepper, thyme, paprika and cayenne in a very large bowl. In a small bowl combine the 1/4 cup buttermilk and the milk. Pour the milk mixture into the flour and use a fork to mix until little lumps throughout.
Heat 1 1/2 inches of oil in a deep skillet or dutch oven over medium high heat to 365F. Working in batches, thoroughly coat each buttermilk-soaked chicken piece with the breading, pressing to adhere the breading. Add the chicken to the oil 3-4 pieces at a time. Cover pan and fry 5-7 minutes, checking to make sure chicken isn’t getting too brown. Turn, cover and cook additional 3-5 minutes more. Monitor temperature of oil to make sure chicken doesn’t burn. Keep in mind chicken will finish cooking in oven.
Place chicken on baking sheet and continue frying rest of chicken. When done, bake the chicken for 10-15 minutes, until chicken cooked through.