Assess the actual condition, immigration permission and proposed activity before relying on the start date. A signed offer does not itself settle every required step.
Explain what is still pending
Distinguish employer expectations from government or licensing decisions. Do not promise an outcome merely to preserve a preferred work date.
Begin with the licensing board, since its processing and meeting schedule usually determines the earliest lawful start and is the part nobody can accelerate. The initial review should produce milestones for credential collection, employer-letter approval, any petition route, travel and permissible start. Work backward from the proposed first day, listing the employer letter, citizenship proof, credential, assignment terms, and intended procedure as readiness gates. If the release falls after the intended start, discuss with counsel and the employer whether the filing or entry attempt should follow the transcript rather than precede it. Once the record is stable, a Canadian outside the United States may request TN classification at a port of entry or the US employer may first file Form I-129; after approval of an advance petition, the Canadian must still seek admission.