@Karen4568 Include it in your house rules. If the CS rep cannot find it anywhere in your listing, AirBnB will not require the guest to honor a late check-out fee.
We do the same as @Lorna170 and put it in the Addl House Rules and we also state that paying the fee does not mean they can extend their checkout time.
Additionally, we also mention the checkout time in our Check-out message and politely remind guests that we do have a late check-out fee, as our cleaners will be arriving shortly after the checkout time to prepare for incoming guests.
What a charming cabin you've got! Are you planning to rent it year-round? I can imagine in winters, it becomes quite magical. ❄️
Lorna and Joan have shared some ideas on how and where you can indicate this fee, let us know if you decide to go ahead that way or would like more advice perhaps!