For principal work at an unaffiliated site, actual supervision and placement purpose need assessment.
Check both offsite conditions
A work start date does not cure an arrangement where the unaffiliated employer principally controls and supervises the worker, or one that is essentially labor for hire rather than a product or service requiring knowledge specific to the petitioner. Review the actual facts and permission before performance.
Allow several weeks to assemble the specialized-knowledge and placement evidence, then USCIS processing time, which premium processing can shorten for a fee. A material change in duties, client placement or employer should be reassessed, since it may affect the basis for the original proposal. Keep the actual approval and status dates on hand, and do not treat a client's delivery deadline as permission to start work whose immigration basis has not yet been confirmed. Decide now who tracks changes to premises, staffing, supervision, and the transferee's actual duties, and agree that material changes go to counsel before they take effect. Ask the employer to name the date the new duties begin and to hold that date until the assessment is complete, and put the request in writing so the sequence remains visible later.