Count backwards from the longest credential step rather than from the travel date. For most listed professions that step is the degree assessment or the state licence, not the immigration presentation itself.
The credential clock usually sets the schedule
Hypothetical example: TN eligibility rests on Canadian or Mexican citizenship, prearranged professional work, and the qualification rule attached to the specific Appendix 2 profession. Two of those three are usually settled early: citizenship is a fact and an offer is a document. The third is the one that moves.
If the profession is satisfied by a degree already held, the lead time may be short. If it is satisfied by a state licence, the applicant is now waiting on a regulator whose processing times are published but not negotiable, and on any examination sitting that regulator requires. A Selwyn surveyor asked to start in spring should therefore begin with the licensing body's current schedule and place every other step to the left of that date.
Working forwards from today's date tends to produce a plan that discovers the constraint too late to accommodate it.