Start as soon as the offer is real. The licence letter, the employer letter and any I-129 filing each take time, and the port-of-entry route needs a complete package on the day of travel.
Sequence the licence letter, the employer letter and the travel date
Hypothetical example: the right-of-way work is scheduled to begin in April and the offer arrives in January. Request the association's good-standing letter first because it is dated and should be recent when presented. Then work with the employer on the letter, allowing for two or three revisions. Decide by February whether the employer will file Form I-129 with USCIS; if so, the filing date and processing time drive travel, and premium processing, where available, is a separate fee on the schedule. If the port-of-entry route is chosen, plan a travel day with time to spare and carry originals. Do not resign from a Saskatchewan position or give notice on a lease until admission or approval is in hand. Build in the possibility that the officer asks for more evidence and that the start date slips by weeks.
Hypothetical example: a survey firm wins a winter bridge-inspection contract and asks the applicant to start the following Monday. The applicant has a licence renewal pending and no final duty letter. The useful decision is to move the start date or choose the advance I-129 route if the employer needs a decision before travel; neither route cures incomplete evidence. At intake, isolate the document with the longest lead time, then set internal dates for the employer letter, credential confirmation, and travel. Keep the intended period realistic rather than copying a hoped-for project duration. Last-minute applications fail when a dated confirmation is stale, a manager cannot sign, or the actual work has changed from the description assembled weeks earlier.