Starpath · Culture and history
The twelve double-hours
A day of twelve two-hour periods, each named for a branch.
Traditional China divided the day into twelve shichen of about two hours. The first, 子, runs from 11 pm to 1 am; then 丑 1–3 am, 寅 3–5, 卯 5–7, 辰 7–9, 巳 9–11, 午 11 am–1 pm, 未 1–3, 申 3–5, 酉 5–7, 戌 7–9 and 亥 9–11 pm.
Your birth double-hour is one of the main inputs of the chart, so a birth close to the edge of a period deserves a careful check.
Many schools count a birth between 11 pm and midnight as the 子 hour of the next day (the “late zi” rule); others keep it on the same day. Astravia shows which rule it used.