Project approval is not immigration permission. The actual offer, credentials and applicable visa or admission steps remain relevant before U.S. work starts.
Separate design sign-off from the employment start
Confirm whether duties or the employing arrangement changed during the project. An internal release date does not settle temporary-entry eligibility or authorize an applicant to begin work while the professional case is still unresolved.
Once a turnaround date is confirmed with the U.S. facility, the support letter, credential evidence and duty description should be finalized well before travel, so the officer reviewing the case at entry has a complete file rather than a promise that documents will follow. In parallel, the offer letter usually needs revision: human-resources departments write to internal templates, and the first draft rarely uses the language the listed profession requires. Ordering official copies from an institution or professional order and arranging certified translation both take time that is difficult to compress, and neither should be squeezed against a start date already promised to an employer. TN admission is granted for a period not exceeding three years and is tied to the employment described, so applying against a schedule that has not settled produces either a refusal or an authorization that no longer matches the work.