You're on last flight of the night, and there isn't much even domestic going out after 23:00. I suspect whatever passes for a CA/*A lounge at KWL international side, will be long closed by that time. As will every other amenity in that facility (there aren't many to begin with). You should therefore maximize your last sightseeing day and activity in the Guilin area, have a good dinner, and push your airport arrival time as late as you can, so you essentially have just a few minutes at the gate before boarding. KWL is a small airport and it shouldn't take too long to check in, esp in Biz Class. Or get through international departures and security. I'd get to the airport about 23:30 or 23:45. Sometime on that last afternoon, you should check status of the OZ departure and make sure time hasn't changed.