Not automatically. The period granted relates to the employment described in the employer's letter, and the officer decides the admission period; it is not set by the applicant's preferred schedule.
Ask for a period that matches real work
Hypothetical example: The employer letter should state the period sought and connect it to the actual duration of the professional work being offered. Where a contract genuinely runs for a defined season, saying so is more credible than requesting the maximum available. Requesting a long period for work that plainly ends earlier invites questions about whether the description is accurate.
Conversely, a period that ends mid-project forces an extension request at an awkward moment, so the letter should reflect the whole engagement if the whole engagement is genuinely arranged. TN status may be extended where the qualifying employment continues, but an extension is a fresh assessment against the same requirements rather than a renewal by default. A Selwyn applicant whose work is expected to recur each season should plan for a repeating decision rather than a single one, and keep the employment record capable of supporting each request.