Leave the unknown part unknown
If you know the birth date but not the time, you can begin with year, month and day pillars. The hour pillar depends on the birth hour. A plausible-looking guess does not turn it into known information.
Wenbu’s unknown-time option omits the hour pillar. The visible-element total becomes six rather than eight, so a temporary calculation reference is not disguised as your birth hour.
Some dates sit on a boundary
A birth on the beginning-of-spring or another solar-term transition date can have more than one possible year or month pillar. The tool uses noon as a provisional reference and discloses the uncertainty; the actual time is needed to settle a boundary case.
Day-boundary schools also differ around 23:00. Without a known time, do not treat a precise hour pillar or detailed timing sequence as established.
Find better information before adding precision
Look for a birth certificate, hospital record or original family note. A recollection such as early morning may define a range, but it does not justify inventing a minute.
Inferring a birth time from past events is an interpretive exercise vulnerable to hindsight. If you compare candidate times, keep the alternatives and the reasons for them instead of saving only the chart that feels most familiar.
Choose an approach that needs less personal data
For a present-day question, I Ching and tarot do not require birth information. They use randomly selected symbols to suggest a perspective, without making reliable predictions about destiny.
A tool that supports the question you actually have is more useful than a fully filled form built on uncertain data.
Sources & further reading
lunar-typescript · calculation source and examples ↗Hong Kong Observatory · Gregorian–Lunar conversion tables ↗Traditional interpretations are not established predictions. See the source notes for context.