When creating a pay, you should be in the PAYE period which is covered by the date that the pay is actually paid to the employee.
The Employers' guide (issued by the Inland Revenue Department (IRD)) states:
"When completing the employer monthly schedule it doesn't matter when a pay period starts or ends. Only include those deductions from gross earnings actually paid or credited to employees during the period covered by the schedule".
A copy of the Employers' guide is available from the IRD website.