Before any date is promised to the customer. Preparation is unpredictable and the qualifying year must fall inside the three years before filing.
Never sell a qualification date against an unfiled petition
Commissioning and qualification work is scheduled around a customer's own installation programme, which creates pressure to commit early. That pressure should not reach the petition. Allow time to retrieve and redact validated files, to obtain customer consent where documents reference their products, and to reconstruct the employment chronology from payroll.
The one continuous qualifying year must sit within the three years immediately before filing, which is a constraint that quietly tightens while preparation drags. USCIS processing follows and can be shortened by premium processing but not removed. If part of the work will occur at the customer's site, the contract establishing that the petitioner directs and supervises the specialist should exist before filing, not be drafted afterwards to match.
Finally, check prior United States time against the five-year maximum before agreeing to a multi-phase programme.