Microsoft is making a change to how it delivers the different types of Office updates each month. As has been the case, the Office teams have followed the rest of the product releases and delivered both security and non-security updates on the same day – on the second Tuesday of each month.
Starting this April (just a few days from now), the Office updates for non-security issues (i.e. bug fixes, enhanced for modified features) will deliver instead on the first Tuesday of each month. So, when April 5 rolls around you can expect an undisclosed number of non-critical, bug fixes.
And, then when the second Tuesday of April kicks off (the regularly scheduled Patch Tuesday, April 12), expect all the security-related fixes for Office to deliver along with the regular round of other product security updates.
For those keeping score, this means that patches will release pretty much all month long now. The first week you can expect Office bug fixes. The second week, the regular Patch Tuesday security updates. And, as has now become tradition, more patches along with Surface firmware updates are made available sometime during the last two weeks of the month. It's like a month of Tuesdays.
UPDATE: This change applies only to the MSI version of Office. Office Click-To-Run (C2R) will release on second Tuesday like normal.
Source: Microsoft Blog