Start gathering the partner's documents immediately, in parallel. Their route may take longer than the principal's, and waiting until TN admission is settled compresses the partner's timeline against a start date that has already been promised to an employer.
Run the two files in parallel from the beginning
The principal's admission does not accelerate anything on the partner's side, so running them one after the other simply adds the two waits together. Begin civil document retrieval and the partner's assessment at the same time as the TN preparation. If one case then stalls, the household still has the other's evidence ready and can decide with real dates rather than estimates.
Keep the employer’s payment date separate from the immigration decision and lawful start of work. Do not start performing the new professional job on the strength of the visitor admission or a pending filing. Ask the employer to move the start date to after the three years are complete. TN admission is granted for a period not exceeding three years and is tied to the professional employment described, so the profession's own qualification rule must be satisfied at the moment the application is made.