There should be 5 because of China's range of longitude.
But on the orders of the central government, the whole country is on Beijing time, so it's all one time zone.
Of course, that means that in far Western China, the sun sometimes rises at 1:00 in the morning and it sets at 2:00 in the afternoon. But that really doesn't upset the government officials 1,000 miles away in Beijing. And you get used to it.