There’s a gremlin in the system! I had my Instant booking changed to accommodate bookings at any time on the same day. I was shocked a couple of days ago to receive a booking at 9.30pm to arrive the same night. I contacted Airbnb straight away and informed them I could not accommodate the booking but I refused to cancel so as not to be penalised. I also contacted the guest at the same time, apologised and told him the system should never have allowed the booking to go through, that I could not accommodate him and he had to cancel to get his money back.
To be fair, Airbnb refunded him the full fees including their fee. They said they would investigate to find out how that happened although I doubt they will update me with their findings since they resolved the main immediate issue.