Function verify_poll_lease_until 

pub fn verify_poll_lease_until(
    state: CreditRegistrationState,
    facts: &RowFacts,
    calls: TimeDelta,
) -> DateTime<Utc>

How long a verify poll pushes a row in state out of reach while its request is out, so a concurrent iteration cannot poll it twice: until its next poll would be due anyway. The poll’s own outcome overwrites this. calls is the longest the iteration’s registry calls may take together: the poll and the recovery lookup after it.