Not before an approved petition exists and the person is admitted in L-1B status. Assembling the specialized knowledge evidence typically takes longer than the adjudication itself, and requests for additional evidence are common in this category, so build a realistic margin.
Expect a request for evidence and schedule as if it will come
L-1B draws additional evidence requests more often than the other L categories, because the standard being applied is qualitative. Planning as though one will arrive is simply prudent: it means the supporting technical documentation is gathered up front rather than assembled under a deadline months later, and it means the business is not depending on a start date that a routine procedural step can move by weeks. The sequence to plan is document gathering, petition preparation and filing, adjudication with or without premium processing, then admission, which for a Canadian citizen follows the approval without a separate visa interview. Do not ship a household or enrol children in school on the strength of a filing receipt.
Hypothetical example: a quarry-dispatch platform analyst is needed for an October software cutover. The review should decide whether technical proof can be prepared before a petition date is selected, using module records, duty description, foreign-service evidence, and project calendar. Work backward from the controlling evidence, then allow time for correction, adjudication, and any admission or consular step. Keep a written chronology of commitments and permissions. The planning failure is that a commercial deadline does not transform generic support into specialized work. Do not let a commercial schedule outrun the immigration record.
Have a technical manager confirm the description before filing.