Early enough that the findings can still change the business. Because the initial new-office approval is limited to one year, the useful review happens with months remaining, not weeks. Financial year-end, bookkeeping schedules, and the time needed to hire a subordinate manager all sit on the critical path ahead of any filing.
Work backwards from the expiry
Mark the expiry date, then place the milestones behind it: financial statements ready, evidence table complete, counsel's assessment delivered, any hiring done, packet reviewed. Leave room for a request for further evidence, which can arrive after filing and consume weeks. Do not treat processing times as something the business controls, and keep customer commitments, travel and family arrangements clear of the period where the outcome is still unknown.
Keep the original submitted plan and record actual staffing, financial and operational developments as they occur, since the extension filing relies on what genuinely happened rather than a restated forecast. For a person initially admitted in specialized-knowledge capacity and later promoted, eligibility for the seven-year total requires at least six months employed in the managerial or executive position, with the change approved in an amended, new or extended petition when it occurs. Periods spent working in the United States for the same employer are excluded from the twelve months, which surprises people whose job already involves regular southbound travel.