File once the year abroad is confirmed and the process description is complete, allow for standard processing or use premium processing, and set the assignment start after the expected approval, not before.
Count backwards from the season, forwards from the year abroad
Two clocks matter. The first is the one-year requirement, measured at filing: the technician must have completed a continuous year of qualifying employment abroad within the three years before the petition, so check the payroll dates first. The second is adjudication time, which USCIS publishes for the form and which premium processing shortens for a fee.
Take the season's first production date, subtract the processing estimate and a margin for a request for evidence, and that is the latest filing date. If the season is fixed and the file is not ready, it is better to plan a partial first season than to file an incomplete petition. Because the technician holds an L-1B, admission after approval is at a port of entry with the approval notice, which for a Canadian citizen requires no visa stamp.
Record the L-1B start date, since the five-year total begins to run from it.