We want to let you know about an important change coming to the release schedule for Office updates so that you can plan accordingly. Until now, both security and non-security updates have been released on the second Tuesday of each month. Starting in April, the non-security updates will be released in Microsoft Update and the Windows Server Update Service (WSUS) on the first Tuesday of the month, which is April 5 in this case. This will include all updates that have the Critical or Definition classification. Updates with the Security classification will continue to release on second Tuesday as usual.

Source: Upcoming change to the release schedule for non-security updates | Office Updates