After the manager has completed a continuous qualifying year abroad within the last three years, and early enough that standard or premium processing finishes before the U.S. operation needs him. Do not file during a period when he is mostly supervising the seasonal crew.
Two calendars: the year abroad and the season
The one-year requirement is tested at filing, so confirm from payroll that a full continuous year in a managerial capacity exists within the three years before the petition date. Then consider the season. If his managerial work is concentrated in planning, contracting and purchasing during the off-season, and the summer is spent on the floor, the description of his role will be more accurate, and easier to support, if the petition is prepared during the off-season and the U.S.
start is timed to the U.S. affiliate's planning cycle. Allow for standard processing or use premium processing, and add a margin for a request for evidence about the chart.
Days he has already spent in the United States working for the affiliate do not count toward the year abroad and should be identified. Once admitted, record the date, because the seven-year L-1A ceiling runs from it.