Is fortune telling based on apparent solar time or Beijing time?

The sun time is accurate. Because fortune-telling books are all ancient, there is no Beijing time in ancient times, so they can only be counted according to local time. For example, it's eight o'clock in Beijing and six o'clock in Urumqi. So should people born in Shandong also follow Beijing time? This is obviously wrong. By analogy, every place is different from Beijing time.

Why do you set Beijing time to facilitate your work and travel, but it is totally unreasonable to look at the eight characters?