I can share a few war stories of long delays of traveling within China and between PEK/PVG and HKG, especially during the summer months. The weather conditions in the summer, for some reasons, have been filled with rains high wind, and storms, and the air space is subject to PLA control.

There was an an article published by AmCham about three years ago. In that article it talks about the split of air space between mililtaty/commerce is about 20/80 in the US. In China, it is the opposite: 80 for military and 20 for commercial.