Before the assignment is offered internally. The calculation depends on documents the individual has to gather, and its outcome determines whether the assignment is possible at the length the business has in mind.
The ceiling is discovered, not negotiated
Unlike most obstacles in this area, this one cannot be improved by better drafting or more evidence. The number is what the history makes it. That makes it the ideal thing to establish first, because it is cheap, quick once the documents exist, and decisive.
Ask the individual to gather the earlier approval notices and passport history at the same time as the initial conversation about the role, and set a date for the answer. If the remaining period is short, the business can consider a shorter assignment, a different candidate, or a different structure while it still has options, rather than restructuring a project after a petition has been prepared. Certainty on this point is unusually cheap and it arrives quickly once the documents are in hand.
Hypothetical example: Yvette is the only technician trained on a company's vibration-analysis library for wind-turbine gearboxes, and a U.S. installation date is fixed. A timing review should identify the last day of the qualifying foreign year, the availability of corroborating technical records, and the date by which the recipient team needs training.
The employment calendar and version-controlled materials set the preparation schedule. Build time to explain any periods spent in the United States. The classification has a five-year aggregate limit for specialized-knowledge transferees, so prior time in that classification must be counted before promising a multi-year assignment.