Allow several weeks to gather corporate and payroll evidence and draft the petition, then USCIS processing time or the premium processing window, then admission at the border or a consular appointment for non-Canadian family members. Start three to four months out for a comfortable margin.
Count backwards, and add the consulate for a non-Canadian spouse
The petition itself is filed once, but the evidence behind it comes from several people: the accountant for share registers and financial statements, payroll for the qualifying year, the Texas landlord for the lease, and the managers for organizational charts. Requesting all of it in the first week is what keeps an L-1A on schedule. Hypothetical example: a Shannon logistics firm wants its general manager in Texas for a warehouse opening in early spring; the ownership and payroll records should be in hand by the end of the year, the petition filed in January, and premium processing purchased if the opening date cannot move.
After approval, a Canadian citizen presents the notice at a port of entry; her British-citizen husband needs an L-2 visa appointment, and consular wait times vary by location, so that step should be booked as soon as the approval arrives. The initial period is up to three years; extensions follow to a seven-year maximum.