For a new office, the lease or other proof of secured premises must exist before filing, so signing comes first. For a transfer to an operating subsidiary, file once the year abroad and the role are documented, then plan travel around the approval rather than the reverse.
Let the evidence requirement set the order
New-office petitions are approved for one year and require evidence that physical premises have been secured, so a company cannot file on the promise of a lease. That forces a sequence: incorporate or register the U.S. entity, open its bank account, sign the lease, then file, and accept that rent may be paid for months before the manager arrives.
Negotiate a lease with a start date or a rent-free period that reflects this. For a transfer into an existing U.S. operation, the constraint is the manager's chronology: the continuous year must be complete and inside the three-year window on the filing date.
Check USCIS processing times and decide whether premium processing is worth its cost. The manager should not resign or sell a house in Sainte-Catherine-de-la-Jacques-Cartier on the strength of a filed petition. Build the extension into the plan from day one, because the first year passes quickly and the extension is judged on what the business actually did.