Acceptance is a business milestone, not immigration approval or admission. Assess the applicable process and remaining conditions first.
Review the dependency behind resignation
Identify what must happen before authorized work can begin and what remains uncertain. Do not treat an employer’s preferred date as a guarantee of government timing.
A port-of-entry application can be decided the same day if the file is complete, so the constraint is usually getting the credential and a correct employer letter together, not government processing. A Canadian citizen presenting at a port of entry pays a modest admission charge; an employer filing Form I-129 pays a filing fee and, if it wants a faster decision, a premium processing fee, both set on the USCIS G-1055 schedule. Applying at the border is faster but leaves no room for a follow-up request; a petition takes longer but produces a written approval before resignation. TN admission is granted for a defined period supported by the employer's letter, and a letter that declines to name an end date invites the officer to ask what temporary means here. A nurse who plans around the immigration step alone will typically discover the gap weeks before a start date, when the remaining steps cannot be compressed.