The requested period should match the actual duration of the professional work and be supported by a project schedule or contract term. Temporary entry is required, so an assignment framed as ongoing territory coverage with no horizon leaves the temporary element undocumented.
Tie the period to the work, not the map
Where the work is project-based, use the milestones to justify the period requested. Where it is continuing, the employer should still state a defined period it can support. Extensions exist and are handled on their own facts, so an honest shorter period is usually easier to document than an indefinite one.
After entry, check the admission record for the period actually granted. Distinguish the period requested from the period actually granted, because only the second governs how long the work may continue. An employer letter proposes a duration; the admission record issued on entry states what was authorized, and the two can differ.
Read that record immediately and diarise its expiry rather than the letter's. Set an extension against a fresh request as well: an extension continues an existing arrangement and is assessed on what the role has become, while a new request starts from current facts. Should a project slip, the question worth asking is whether the work still matches the profession claimed.
A schedule change that quietly converts advisory work into operational cover is a substantive change, not a calendar one.