In a bowl, mix together the buttermilk and salt. Add the chicken tenders and mix, being sure the chicken is evenly coated with buttermilk. The chicken should be at least halfway submerged in the buttermilk so add more if you need to. Cover with plastic wrap and transfer to the refrigerator overnight or for a minimum of 3 hours.
Preheat the oven to 200 degrees F. Remove the bowl of chicken and allow to sit on the counter while you prepare everything. You don't want the chicken freezing cold.
To a medium pot or cast iron, add enough oil so it reaches 1 1/2-inches up the pot's side. Heat the oil to 325 degrees F to 350 degrees F. While the oil is heating up, mix together the flour, salt, pepper, thyme, paprika and cayenne. In a super small bowl, mix together the buttermilk and milk; add it to the flour mixture and mix. (This will make the flour mixture a little shaggy which will help with the crispiness.)
Prepare for a double-dredge! Working in an assembly-type fashion, thoroughly coat each buttermilk-soaked chicken tender with the breading. Re-dip it in the buttermilk and coat it one more time with the flour mixture, pressing to adhere the breading to the chicken tender. Add the chicken to the oil 3 pieces at a time. Allow to fry for 2-3 minutes and until golden brown. Remove and drain on a paper towel. Transfer the fried chicken to a baking sheet and place in the oven to keep warm while you make the waffles.