Yup. I get a fair few of those requests for a rather inconvenient check in time. Like you, when I get the booking, I ask for an approximate arrival time - Hey: Air BnB didn't this used to be a 'must tell' thing?! - and remind them of my check in time. Sometimes that's when they mention the midnight arrival.
I have now written a standard "Here is a list of the hotels near the airport with 24 hour check in faciliites" document which I copy and paste into the Air BnB messages. I also add this little gem "Please do not arrive at my home after 9pm as there will be nobody there to let you in." So far, this has worked for me. And it covers my butt if the guest complains to Air BnB.
Could you add something to your house rules (and remind them when you acknowledge their booking) stating that you require them to send you their flight/train number (or approximate arrival time if using their own transport).
As an aside, the phrase "If you send me your flight number, I can watch online for any updates, so that you do not need to worry about trying to let me know of the changes." has the double benefit of removing the stress from the guests and for the hosts, it is a subltle way of saying "Don't try using the old My Flight Was Delayed excuse for a rediculously late arrival!
Good luck with that guest arrival!