Payrolls can only be reopened up until their reopen_deadline, which is calculated after it is approved. After the reopen_deadline is passed, the payroll will move from a pending to a processing status, and can no longer be reopened (because it is has begun being processed by Check).

In general, the reopen_deadline for a payroll is set to 1 hour after it is approved, or the payroll's approval_deadline, whichever is earlier.

In addition, the earliest that the reopen_deadline can be is 11am ET on the day of the approval_deadline. In other words, if a payroll is approved several days in advance of the payroll's approval_deadline, then the payroll will still be able to reopened until 11am ET on the day of the approval_deadline.