The state licence sets the schedule and commonly takes months. The immigration step is comparatively short, so plan backwards from the board rather than from the border.
Plan from the licensing board's queue, not the employer's preference
Three things must be in place before travel, and they move at very different speeds. The state occupational therapy licence depends on the board's processing, on verification sent directly by the Newfoundland and Labrador regulator, and on examination records; that is the long pole and it is outside anyone's control. The employment documentation depends on the staffing company, and getting an agreement that clearly identifies the employer and the placements often takes several exchanges.
The TN application itself is decided at the port of entry the day it is made, or takes USCIS processing time if the employer petitions instead. Do not resign a Canadian position or commit to a move until the licence has issued and the employment terms are settled in writing. A start date agreed in a recruitment call is not a commitment either side can keep on its own.