It is measured in years rather than months: adjudication of the investor petition, then the immigrant visa or adjustment stage subject to visa availability, then two years of conditional residence before conditions are removed. Published processing times and the Visa Bulletin govern the middle stages.
Three stages, each with its own clock and one outside anyone's control
The first stage is the investor petition, whose processing time USCIS publishes and revises. The second is obtaining the immigrant visa or adjusting status, which depends on visa availability by country of birth; where demand exceeds the annual limit, applicants wait for their priority date to become current in the Visa Bulletin, and that wait is not something any adviser can shorten. The third is the two-year conditional period ending with a petition to remove conditions, which itself takes time to adjudicate. Two planning consequences follow. Children age during the process, which is why the age analysis belongs at the start. And the capital stays invested and at risk throughout, so it should not be money the family needs for anything else in the meantime.
Hypothetical example: a musical-instrument restoration owner wants a child to begin university next year. The review should decide whether petition, availability, residence, and condition-removal stages fit that date, using birth evidence, current availability data, petition calendar, and I-829 planning. Work backward from the controlling evidence, then allow time for correction, adjudication, and any admission or consular step. Keep a written chronology of commitments and permissions. The planning failure is that investor petition approval does not itself deliver immediate residence. Do not let a commercial schedule outrun the immigration record.