Your birth time is what pins the sky's rotation to the horizon. The date tells us where the planets were; the time tells us which way the Earth was turned underneath them. Lose the time and you lose the rotation — which means the rising sign, the houses, and anything built on them can't be computed honestly.
So Bob won't fake it. Instead of quietly defaulting your birth time to noon and handing you houses that are probably wrong, he tells you exactly what's off the table and gives you everything that's still real. A birth certificate upgrades the whole chart later.
Needs your birth time
- Rising / Ascendant
- All houses
- MC & IC, angle aspects
- Part of Fortune
- Most of Human Design
- Profections
- Solar-return houses
- Zi Wei palaces
- BaZi hour pillar
Sometimes uncertain
- Moon sign & Vedic nakshatra — only if you were born within ~½ day of a sign change
Rock-solid without it
- Sun sign
- Mercury–Pluto signs
- Planet-to-planet aspects
- All of numerology
- BaZi year / month / day pillars
Born within about half a day of a sign change? Your Moon sign (and Vedic nakshatra) can be uncertain too — Bob flags that specifically rather than picking one.