Wait until the date is firm before presenting anything. TN admission is granted for a period not exceeding three years and is tied to the employment described, so applying against a schedule that has not settled produces either a refusal or an authorization that no longer matches the work.
Apply to the timetable you can actually document
Delay is manageable; applying into a delay is not. Oluwaseun should treat each postponement as a trigger to reconfirm three things with the employer: what he will do first, when he will begin, and how long the assignment is now expected to run. Only when those answers hold still should the letter be finalized and the application made, whether in person as a Canadian citizen, who needs no visa stamp, or through an employer petition presented at the port after approval.
Two traps are common in the interval. Beginning work remotely from Ontario for the U.S. entity raises questions about who employs him and when the employment started.
Travelling to help commission the line as a visitor, then performing productive work, is a different problem again. Neither should be improvised without advice.