The "hou" (period) comes after the 24 solar terms, and the Chinese people further divided the solar terms into hou, which is a smaller unit of the lunar calendar.
Originally, starting from the beginning of spring, each hou was five days, making a total of 73 hou in a year (the last hou being six or seven days). This was a simple "ping hou" (equal period), similar to the "ping qi" (equal term).
Later, it combined with the 24 solar terms, eliminating one hou, resulting in 72 hou starting from the beginning of spring, i.e., "three hou per solar term," becoming a refined unit of the solar terms. In this way, equal periods corresponded to equal hou; the hou corresponding to the determined periods was called "half-determined hou."
The ancient calendar expert Liu Chuo proposed the "determined hou." In modern terms, this means that each hou corresponds to every 5 degrees of the ecliptic, not necessarily five days.
The current lunar calendar in China uses determined periods and determined hou.
Although these various hou may not all be five days, as a time unit, "hou" is considered five days.
Personally, I believe there is another type of "standard hou," similar to the modern "xun" (ten-day period). One solar term consists of three hou, with the first two hou being five days, and the last hou lasting until the day before the next solar term.
Hous are essential supplements to the solar terms. Together with the 24 solar terms, they form the solar components of the Chinese lunar calendar. It is a unique solar calendar system in the Chinese lunar calendar and an important idea and spiritual wealth of our culture.