Five years at most in L-1B, and the placement itself has to satisfy separate conditions throughout. The petitioner must continue to control and supervise the work, and the arrangement must not be labour for hire, so the answer depends as much on the services agreement as on the calendar.
Five years, and who controls the day
Two clocks run at once. One is the classification limit, which counts every period already spent in L status and does not restart with a new petition. The other is the durability of the placement itself: an arrangement that begins with the petitioner directing a defined project can drift, over a couple of years, into the customer setting daily priorities and the petitioner simply invoicing for time. That drift is a status problem before it is a contractual one. Review the arrangement annually against what the petition described, and document the review, so a change is caught while it can still be corrected.
Hypothetical example: a controls specialist from Roxton Pond is placed almost entirely at a customer’s sawmill in the United States to integrate a scanning and optimisation platform. The petition describes a defined integration project with milestones, supervision by a Canadian engineering manager, and deliverables owned by the petitioner. Two years later the customer has begun assigning unrelated maintenance tasks and the milestones have lapsed. Restating the deliverables in writing, and restoring a real reporting line, is the response; letting the drift continue quietly is how a placement stops resembling the petition that supports it.