The IRD are in the process of replacing their mainframe system and improving their business processes. This year's outage is scheduled for 1500 Thursday 9 April 2020 through morning of 16 April 2020. Online and phone services are unavailable through this time.
The main payroll related benefits you will see are:
KiwiSaver contributions and deductions will get to providers faster
PAYE payments will be allocated and reconciled faster
Your account in myIR will be easier to understand
Notifications from the IRD will be in a better format.