Why was it beheaded at three o'clock at noon in ancient times?

There is a saying in the old novel called "chop at noon three times", that is, chop at noon three times (fifteen minutes away from noon). At this time, the yang is full and the yin is dissipated immediately. This heinous crime should be "not even allowed to do ghosts" to show severe punishment. Yin and Yang experts say that Yang is the most abundant, which is different from modern astronomy. Not at noon, but at three o'clock. In ancient times, beheading was carried out in different periods, that is, beheading was important. Generally, beheading is to operate at noon and let it have a ghost to do; Repeater or heinous criminals must choose the operation at 3: 30 noon, and don't let it be a ghost. The meridian gate of the imperial city is also the most prosperous, regardless of time, so the emperor ordered the people who started the meridian gate to behead, and no ghosts did it.