Long enough to form the entity, sign a lease, gather three years of payroll and prepare the petition before filing, plus USCIS processing time and, for a Canadian citizen, the border or consular step. The opening date should be set after the approval notice, not before.
A realistic sequence
Treat the process as three blocks. The first block is corporate and commercial: forming the U.S. entity, funding it, negotiating and signing the lease, and confirming the director's qualifying year from payroll.
That block is entirely within the company's control and typically takes the longest. The second block is preparation and filing: the business plan, the organization chart with hiring dates, the ownership chain, and the petition itself, with premium processing available if the company wants a faster decision. The third block is admission: a Canadian citizen may present the approval at a port of entry, and the family follows on L-2.
Then the clock that matters starts, because the one-year approval means the extension petition must be prepared from month nine using real operating records. Companies that sign customer commitments for a facility opening on a date chosen before filing usually end up renegotiating them; a director with a cross-dock waiting cannot begin managing it until the status exists.