I do remember checking in at Xian a few years ago before KA stopped flying there the first time, and check-in didn't open until either 2 hours or 90 minutes before departure.
Most "secondary cities" in China don't allow "international check-in" until 90 minutes before departure. This is common practice in China. As their custom agents, People's Liberation Army, border control agents don't show up to their posts until 90 minutes before check-in.
This is why I don't get to the airport until 40-45 minutes before departure if I need to fly out of secondary cities, if you arrive early there will already be tons of people showing up trying to rush in as soon as they let you, and you will be waiting in line anyway. Might as well get there later, when the rush is over, and check-in without a line. (Of course now your local traffic well, if you are stuck in traffic then you're out of luck.)