Begin as soon as the transfer is contemplated. The corporate evidence and the employment chronology usually take longer than the petition itself, particularly after a restructuring.
Start where the records are, not where the calendar is
Hypothetical example: Three things set the schedule and only one of them is government processing. The first is the corporate chain: obtaining certified registers and resolutions from a lawyer or accountant can take weeks, especially if the reorganisation was handled by a different firm. The second is the employment chronology, which must show one continuous year with a qualifying entity inside the three years before filing.
If the manager spent months seconded to the American company, that time does not count toward the year, and discovering it late can mean waiting until a fresh qualifying year accumulates. The third is USCIS processing, which premium processing can compress but not eliminate. Do not set an installation season or a customer commitment against an unfiled petition.
A new-office petition, if the American entity were newly formed, would carry its own one-year approval limit and a different evidence set.