This is an issue I've reported to AirBnB 10+ times over the last 5 years via feedback form, chat, and phone calls. It's unlikely to ever get fixed but maybe they'll look into it if enough other hosts report the same issue.
The attached screenshots pretty much sum up the problem. My place has a check-in time of "after 3PM" but whenever I get booking within the next 24 hours, the booking confirmation that comes through includes a guest-selected check-in time that is generally before the time shown on the listing.
How do other hosts deal with this? If I tell the guest "sorry the place can't actually be ready by the time you selected, even though the website displayed those options as valid selections", that definitely sets things off on the wrong foot.
@Nick @Lizzie