I sometimes think it is easier of you are not on site, no show nobody to let anybody in and a lockbox strikes me as being too risky for my taste.
There is no easy answer, I used to have 11pm and moved it back to 10pm on the basis anybody turning up late would in most cases be there within an hour.
I also message guests with the very basic information a day or so before their trip, and ask for their approx arrival time.
I still get enquiries for my cheapest room for a night on the lines of our plane arrives at 9.30pm whatever in Denver, well an hour to get through and to car rental, 2 hours to get here so no, suggest they look for somewhere near the Airport.
There will occasionally be a late arival with a valid reason, my last late ones came in at 1.30 am in May in the middle of a blizzard wearing flip flops and shorts.. They all have phones, they can see their eta and the weather.
David