Do not assume that. Review the changed arrangement and actual permission before the activity begins.
Align the transaction with immigration assessment
A commercial effective date is not a government decision. Explain changed duties or entities before relying on an earlier file.
Allow time for the credential review and the employer letter, then decide whether a same-day port-of-entry application or a petition with a written decision suits the risk. A Canadian citizen can apply at a port of entry the day the file is complete and, if admitted, begin work immediately, so the timeline is set by how quickly the supervising professional's letter and credentials are assembled. Recheck current admission procedures before travel, and ask for a fresh review if the employer, duties or assignment changes. TN preparation and the actual government decision are separate steps, and an expected date does not itself authorize work. Canadians generally request TN admission at a port of entry or have an employer submit Form I-129; neither occurs automatically when a scheduling email names a site.