A double-hour is not a clock time
People often get stuck at the same place when entering a birth time. Some tools ask for hours and minutes, some ask for a 時辰 (shichen, a traditional two-hour period), and some ask for both plus a birthplace. Which is right?
The short answer: these are two different routes, and they must not be mixed.
A shichen is solar time; a clock reading is administrative time
When classical texts say 巳時 (si hour), they mean the stretch of the day when the sun sits in a particular place. That time follows the sun. It is already local and already astronomical.
When we say "9:30 in the morning" we mean a civil time zone reading. The whole of China runs on Beijing time: clocks in Chengdu, Ürümqi and Harbin all strike nine together, yet the sun's actual position differs by tens of minutes between them.
So:
- If you give a clock reading, we need your birthplace to convert that administrative time back into local solar time. That step is called true solar time correction.
- If you give a shichen, the time is already solar. Applying a longitude correction on top would treat it as a clock reading a second time.
What goes wrong if you convert it anyway
Chengdu runs about 56 minutes behind Beijing time.
Someone says they were born in the si hour, which runs 9am to 11am. If we mistake that for a clock reading and subtract Chengdu's 56 minutes, it lands in the chen hour instead.
That changes the hour pillar. The hour pillar governs children, later life, and part of the strength judgement. Change that pillar and the conclusions downstream move with it.
So this is how Guanming asks
| How you enter the birth time | Birthplace asked? | True solar time applied? |
|---|---|---|
| Exact hour and minute | Yes, skippable | Only if you give it |
| A shichen (si, wu, …) | No | No |
| Hour unknown | No | No |
Pick a shichen and we cast exactly that shichen, with no conversion at all. That is deliberate, not an oversight.
Which is more accurate
If you genuinely know the clock time, enter the exact time and select the birthplace. That route carries the most information and gives the most reliable hour pillar, especially for people born near a shichen boundary.
If your family only remembers "born in the si hour", choose the shichen. Inventing a clock reading to look precise only adds an error that was not there before.
What if the hour is unknown
Choose "hour unknown". Guanming casts the first three pillars using noon as a placeholder and states plainly in the report that anything derived from the hour pillar alone is withheld: children's fortune, later-life fortune, and part of the strength judgement.
Better a gap than an invention. A children's palace computed from a fake hour pillar looks convincing and is simply not true.