子時換日 (Zi-hour day boundary)

• 中文 / Chinese: 子時換日

The Palm Sutra fixes the Day pillar from the lunar day. The Zi hour spans 23:00–01:00; the 23:00–24:00 "late Zi" is assigned by some schools to the current day and by others to the next, which shifts the Day pillar and the Hour pillar that follows it.

Conventions 各派做法

• Same day (common) (當日子時（通行）) — default — Late Zi stays on the current day; the whole Zi hour uses the current day pillar.
• Late Zi rolls over (夜子換日) — Late Zi (23:00–24:00) rolls to the next day; the day pillar advances before the Zi hour is taken.

The reading tool lets you pick the convention; the first option is the common default. Different choices can shift the pillars for births at late Zi or in a leap month.

All schools & conventions · The four pillars · Palm Sutra knowledge base

機器可讀原始檔（供 AI 檢索）：/okf/yizhang/schools/zi.md