No. Timelines vary with the applicable route, the completeness of the evidence, and factors outside the applicant's control, and no one can promise a decision by a given day. An agreement that assumes a fixed resolution date is assuming something that cannot be guaranteed.
Negotiate around uncertainty rather than predicting it
Because the route that applies depends on citizenship and current circumstances, and because each route has its own steps, a single promised date is not something counsel can responsibly supply. The practical response is a contract that accommodates variance: a start date defined by authorized entry, a repayment clause that excludes delay outside the applicant's control, and a written extension mechanism.
Ten weeks accommodates the petition route with premium processing and leaves time to correct a problem; it is ample for the border route if the documents are already consistent. TN preparation and the government's actual decision are separate steps, and an anticipated date does not itself authorize work. A Canadian may seek TN admission at a port of entry or rely on an employer’s Form I-129 procedure, but neither route should use a terminated assignment. The timing of entry, commencement and any material change should be planned around the applicable authorization.