Before the U.S. project needs the person. Evidence gathering and any repair to the qualifying year set the schedule, and neither can be accelerated at the end.
Evidence gathering sets the calendar
A transfer request that arrives with a project already underway creates pressure to file a thin case, which is the worst version of this classification. The realistic preparation window covers assembling contemporaneous technical records, confirming the ownership chain between the two organizations, and verifying that the continuous qualifying year is unbroken on the payroll as it actually ran rather than as it is remembered. Any of those can add weeks.
Where the U.S. operation is itself new, a new-office approval is normally limited to one year and requires evidence of secured premises and capacity to support the role, which creates a separate lead time running in parallel. Set the project schedule around the slowest of these rather than the other way around.