add new behavior to global-important-changes

Author: kpcraig

content/vault/global/partials/important-changes/summary-tables/1_21.mdx

@@ -7,7 +7,10 @@ Introduced | Recommendations | Edition    | Change
 
 ### New behavior
 
-None.
+Introduced | Recommendations | Edition    | Change
+---------- | --------------- | ---------- | ------
+1.21.0     | **Yes**         | Enterprise | [Rotation manager schedule strings in UTC](/vault/docs/v1.21.x/updates/important-changes#rotation-manager-utc)
+
 
 ### Known issues