Don't start any money transactions outside of Airbnb, it will only cause you problems, especially if you are already in a problematic situation with a guest.
I see that regarding check in and check out times, you only have check in times stipulated from noon to 6pm, nothing under check out times. To protect yourself, how about stipulating a check out time like 11 am? Most hosts don't go later than that, and you can always make special arrangements with a guest, but then it is clear what is expected. You might also rethink your check in times, perhaps a bit later and extending to 8 pm, like 3 pm to 8 pm? As you have it now, what would you do if a guest leaves at 6pm, but a new guest has booked for that day and wants to check in at noon? nevermind the time you need in between to clean...
Just a suggestion, good luck and happy hosting!