Practice authorization from the state regulator typically governs, since relief shifts cannot be worked without it, and that process runs on its own schedule. The immigration route is a separate sequence. Neither should be compressed to meet a shift already placed on a clinic's calendar.
Two independent sequences, both before the first shift
Begin the licensure file as soon as the destination state is settled, because verification from an institution or a home-jurisdiction regulator involves third parties. In parallel, have counsel confirm what the applicable route requires for the applicant's circumstances. Tell the agency or clinics that shift assignments should stay provisional until both are resolved, rather than accepting bookings against an estimated date.
Employers can usually adjust a role before it is posted internally or budgeted, and much less easily afterward. Payment of a moving allowance is not US admission or work authorization. A planned review or signed offer is not permission to begin. An employer’s recruitment timetable does not authorize work before the immigration basis is established. Coordinate the actual start with the authorization and role that have been assessed. Do not begin work merely because travel has been booked.