The first, seventh, fourth and tenth of the Earth's branches. When using the Earthly Branches to keep track of time, "Zi Wu" refers to the period from midnight to the middle of the next day, and "Mao You" refers to the period from sunrise to sunset.

Afterwards, it was used to indicate the sequence of time or to record the number of degrees of orientation.

It is also used to indicate the detailed process of things before and after.

The Zi, Wu, Mao, You, in the twelve hours, exactly when the yin and yang meet. Zi time, is the previous day and the day after the handover moment; noon, is the morning and afternoon handover moment; Dao time, is the sun rise before to rise time; You time, is the sun has not yet set and set time.

Extended information:

The general name of Zǐ, U (chǒu), Yin (yín), Mao (mǎo), 辰 (chén), Si (sì), Wu (wǔ), Wei (wèi), Shen (shēn), You (yǒu), Xū, and Hài (hài). Also known as the twelve branches. In ancient China, the twelve Earthly Branches were used to mark the time and month.

The earth's branch is divided into 12 periods of time, respectively, the twelve earth's branches, the son of 23 ~ 1 time, the ugly time for 1 ~ 3 times, and so on, known as the twelve hours. The month in which the winter solstice occurs is called the Zi month, the next month is called the U month, and so on.

The earth's branches are matched with the order of the ten heavenly stems to form A Zi, B Chou ...... Dec Hai, which are used for days and years in a cycle of sixty.

Twelve Earthly Branches: Stem Calendar will be divided into twelve eons a year, "Jian" on behalf of the Big Dipper seven stars at the top of the handle pointing to; ancient astronomy said the Big Dipper handle pointing to the "Jian", a year of the handle rotating and pointing to the sequence for the "The twelve eons of the year are called the "Twelve Months of the Dipper" (or the "Twelve Months of the Dipper").

December Jian is based on the twenty-four seasons of the festival month, is a solar month, different from the lunar month (the first day of the month, divided into the first fifteen, etc.), with twelve branches of the earth, such as Jianzi, Jian丑, Jianyin, and so on.

Baidu Encyclopedia - Zi Wu Mao You