What is a three-day holiday and when?

Three broken days are every Jiazi year (the calendar of Shang Dynasty adopted the "heavenly stems and earthly branches" 60-week calendar. The heavenly stems are "A, B, C, D, E, G, Xin, Ren and Gui" and the earthly branches are "Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai". Starting with the first word "A" in the heavenly stems and the first word "Zi" in the earthly branches, take one word in turn and combine it into Jiazi, Yechou, Bingyin and ......................................................................................................................., and then start a new cycle from Jiazi.

In the thirty years of Jianwu in the Eastern Han Dynasty (AD 54), only 60 branches were recorded. This is the chronology of branches. Each cycle must start with "Jiazi" and be called "One Jiazi" or "One Flower Jiazi" after 60 years. How do we convert the year into branches? Because the chronology of Ganzhi began in the thirty years of Jianwu in the Eastern Han Dynasty (AD 54). The third year of AD is the year of Guihai, which is the last year of 60 Jiazi, so the next year is the year of Jiazi, which is the beginning of a new cycle. Therefore, the remainder R is obtained by calculating (AD 3) ÷60. The remainder R÷ 10 is X, and the remainder R÷ 12 is Y.) Once, on that day, those ghosts and evil spirits were very angry, they could not survive, and they could not get sacrifices from their relatives. That day is often the night when ghosts walk at night and are reborn, so in the past, adults at home would never let their children go out on this day. Everyone closed the doors and windows and waited with all the lights on.