Google it, its been the case for years. Every major airline does it at one time or another. Not necessarily on every flight, and I would doubt they would do it to PEK, but the practice is widespread. FYI, the atc situation in China is a mess. On the day I went from SHA to PEK every flight was delayed or ground held. The excuses were everything from weather to military necessity.
The natives took it in stride, in China domestic departure times are usually found in the fiction section.