Longer than any single stage suggests. Preparing the source-of-funds file alone takes months. Petition processing, visa availability for the applicant's country of chargeability, two years of conditional residence and then the petition to remove conditions each add their own period, and only the last of these is within anyone's influence.
Plan the sequence around the parts you cannot control
Halvard should treat the timeline as three blocks. The first is preparation, where the work is his: gathering records, obtaining valuations, completing diligence on the project. This block is the one people compress and the one that most repays patience, because errors here surface much later.
The second is adjudication and visa availability, which depends on processing and on demand from applicants chargeable to the same country, and is simply not controllable. The third begins on admission: conditional residence runs for two years, and Form I-829 is filed within the ninety days before the second anniversary of obtaining that status. The capital must remain invested and at risk for the period the law requires, which should be confirmed against current official guidance.
Selling a business to fund an application that has not yet been made is a decision to take with advice, not in sequence.