File once the corporate and employee records are complete, allow USCIS processing or premium processing, and set the start date after approval. An established subsidiary can request up to three years initially, with extensions to a seven-year maximum in L-1A status.
Approval first, then the start date, with the cap in view
Hypothetical example: the company wants the director in place before a large customer's implementation begins. Because the U.S. subsidiary has been operating for two years with its own lease and staff, the petition is not a new-office case, and an initial period of up to three years may be requested; a new office would be limited to one year.
Extensions may be granted in increments of up to two years, up to a total of seven years in L-1A status, and any earlier time in L or H status counts against that total, so gather the director's U.S. status history before promising a long assignment. Schedule the filing so that current USCIS processing time, or premium processing, ends before the customer implementation; do not have her start work in the United States before approval.
The initial petition must establish the one continuous qualifying year abroad within the applicable three-year period; an extension does not restart that rolling three-year test, although the qualifying relationship and both companies' active operations must continue.