Administrative onboarding is not the same as beginning employment, but the line is easy to blur when a portal starts assigning tasks. Work should not begin before the applicant is authorized, and a filed application does not by itself provide that authorization.
Set the actual first workday deliberately
Ask the operating company to record a start date that follows admission or the effective date of status, and to hold off on assigning substantive work before then. Clarify which onboarding steps are purely administrative. If the payroll system pressures an earlier date, raise it with counsel before accepting it, since an early start is difficult to explain afterwards.
Work backwards from the day the professional may lawfully begin rather than forwards from the day the portal opens. Fix three dates in order: when the operating company needs the work performed, when admission or the effective date of status can realistically occur, and only then which onboarding steps must precede either. Where a project phase gate falls before that date and the professional is expected to attend, ask the operating company to characterise attendance as observation or as work, in writing, before the meeting happens.
An authorized period also ends on a stated date. Put the extension question in the corporate calendar well ahead of it, because work continued past that date is not repaired by a filing made afterwards.