Before filing, while the actual staffing and decision allocation can still be described truthfully.
Use the filing as a planning deadline
Fix the staffing picture before the petition is signed, because the description has to be true on the filing date rather than aspirational. Three items usually set the critical path. Corporate records proving the qualifying relationship can take weeks to retrieve when ownership runs through more than one entity.
The foreign payroll evidence must cover one continuous year of full-time qualifying employment falling inside the three years before filing, and that window closes with time, so a transferee who has already spent months working in the United States should have the count checked early. For a new office the lease and the hiring plan must be real before filing, not afterwards. Then choose the processing path: regular adjudication or premium processing, with consular or border processing for the entry once the petition is approved.
A new-office approval runs one year, so evidence for the extension, meaning actual staff, actual revenue and a role that remains primarily managerial or executive as described, accumulates from the first month rather than the eleventh. Track cumulative time against the seven-year L-1A maximum, counting earlier L stays. If duties change materially after filing, treat that as a present question and take advice then, because the earlier letter does not keep proving a structure that no longer exists.
Confirm sequencing with a U.S.-licensed immigration lawyer.