Zi Hour Day Change
Problem
Zi hour straddles midnight (about 23:00–01:00). If birth falls here, the day pillar may follow two schools:
| View | Practice |
|---|---|
| Night Zi changes day | From 23:00 use the next day’s day pillar |
| Early Zi does not change / midnight change | Before 00:00 keep today’s day pillar; change after 00:00 |
The hour branch is still Zi; the dispute is whether the day stem–branch advances.
Decision steps
- Normalize birth time to charting time (including time zone and optional true solar time).
- If the moment is in the Zi interval, mark as borderline.
- Explicitly choose one rule above and compute the day pillar.
- Record in the result:
zishiRule = night-change | midnight-change(or equivalent). - For important conclusions, optionally list the day pillar under the other rule for human choice.
Impact scope
- Day pillar change → Day Master change → whole-chart Ten Gods may need recalculation.
- Hour stem is escaped from day stem; day stem change usually changes hour stem too.
So Zi-hour rule is not a detail—it is part of the chart’s identity card. See Four-Pillar Charting.
Boundaries
Both schools are in use. This library does not force a single truth, but forbids silent mixing.