Start the health-care certificate and state licence processes as soon as the offer is serious, typically several months before the intended start, because both depend on third parties. The border application itself is decided at the port of entry on the day of travel once the documents are complete.
Sequence the slow third-party steps first
The TN admission is fast; everything feeding into it is slow. Credential verification organizations request records directly from the nursing school and regulator, and each institution responds on its own schedule. State boards may require fingerprinting, verification of the Ontario licence and an examination result before issuing a permit. Karina should build the timeline backwards from the contract start date, place the certificate and licence applications at the front, and treat the employer letter as the last item to finalize, so it reflects the licence she will actually hold. A resignation from her current position should wait until the certificate and licence dates are confirmed. If a start date cannot move, ask the employer whether an orientation role that does not require the state licence can bridge the gap, and have counsel check that any such role still fits the profession.
Hypothetical example: A statistician is expected to begin a research contract six weeks after accepting an offer. A first review works backward from the proposed start date and identifies the slowest item, often a licence, health-care certificate or original academic record. The employer should not set travel until the evidence is assembled and the role description is final. If it chooses a USCIS petition, build in time for the agency process and any request for evidence. Rushing with an incomplete package can create a refusal that a better sequence would have avoided.