That depends entirely on the employer's policy and payroll cycle, so ask for the specific sequence: claim submission, approval, and the pay run it attaches to. Treat any date as an estimate until the employer confirms it in writing.
Ask for the sequence, not a date
A single promised date hides several steps that can each slip. Asking who approves claims, how often approvals run, and which pay period a claim lands in produces a range the household can plan around. Combine that with the point at which work may lawfully begin, which is set by the authorization steps rather than by the employer's calendar.
The specific error is treating one date as if it governed two different things. An employer's start date sets when the role is expected to begin; whether work may lawfully begin is decided by the authorization steps, and no filing or application permits work while it is pending. Households that miss this book the removal van against the wrong date.
Write the sequence out with an owner beside each step — who requests, who approves, whose calendar the step sits on — and you will see which parts the employer can accelerate and which it cannot. Then ask the payroll question separately: which cut-off a first claim must reach, and what happens to a claim that misses it by a day.