How to chart the early and late zi hour

The earthly branch rat covers two hours: 23:00 to 01:00 the next day. The clock changes the date at midnight, so that same stretch is cut in two: 23:00–00:00 is usually called the late rat hour, and 00:00–01:00 the early rat hour.

Both halves have rat as the branch — that is not the problem. The problem is the day pillar. The rat hour opens the twelve hours, and tradition usually counts the rat hour as the start of a new day rather than waiting for midnight.

So a birth at “11:20 in the evening” is still the same day on the household register, while the chart may already be using the next day's day stem. Once the Day Master changes, the Ten Gods, the configuration and the starting point of the luck cycles all move with it.

The common Zi Ping method changes the day at 23:00. The late rat hour (23:00–00:00) and the early rat hour (00:00–01:00) use the same next-day day pillar, and the hour pillar is rat in both.

A comparison: born at 23:20 on 12 May 2024 by the clock. With the 23:00 rule, the day pillar is 13 May and the hour pillar is rat; with the midnight rule, the day pillar stays 12 May and the hour pillar is rat. The two charts can have completely different Day Masters.

Now take 00:20 on 13 May: under both calculations the day pillar is the 13th and the hour pillar is rat. What really comes down to a dispute is almost always the single hour between 23:00 and midnight.

A third school splits the rat hour itself: the first rat (子初, 23:00 to 00:00) keeps the day pillar of the same day but takes the stem of the next day's rat hour, while the second rat (子正, 00:00 to 01:00) uses the next day for both. This is the early/late split. 问真岛 does not use it, so that one moment never produces two different day pillars.

Enter the actual time from the hospital or the clock — to the minute if you can. The system draws the day boundary at 23:00: 23:00–00:59 belongs to the rat hour of the next day, and the day pillar uses the next day's stems and branches.

If true solar time is switched on, first check whether the corrected moment has crossed 23:00. In Chengdu, a clock time of 23:20 minus about 64 minutes gives 22:16, which falls back into the pig hour of the same day — and the day pillar returns to that day too. In Shanghai, 23:20 is only a few minutes off and most likely stays in the next day's rat hour.

If the birth certificate says 23:00 sharp, treat the minutes either side as a boundary. After charting, look at the stem of the day pillar: if it does not match the birthday you remember, check first whether the 23:00 rule applies, then check true solar time — and only then consider changing the hour.

If you only remember “close to midnight” but not the minutes, chart 22:40 (pig hour, same day) and 23:20 (rat hour, next day) separately. The parts both charts share are the steadier ones; where the Day Master differs, mark it as pending verification.

Verify the hour against events that already happened: entering school, moving house, surgery, marriage, starting a job. See which chart explains your experience better, not which one sounds luckier.

With no record at all, chart a three-pillar reference chart from the clock date and mark both the hour pillar and the day boundary as pending. The rat-hour question is a date boundary, not a mystical switch.