In Workday Adaptive Planning, before changing the default time stratum of an instance, all standard account data must be deleted. This is a prerequisite enforced by the system because the time stratum fundamentally defines how data is stored and aggregated across time periods. Standard account data is structured according to the current time stratum, and changing the stratum without clearing this data would create structural inconsistencies and orphaned data records that the system cannot reconcile. Once the data is deleted, the administrator can change the default time stratum and rebuild the time structure. This is why changing the default time stratum is considered a significant, typically one-time implementation decision that should be made before data is populated. Setting the stratum to a specific value, deleting the calendar, or appending the calendar are not prerequisites for this change - the critical precondition is the deletion of existing standard account data. Reference: Workday Adaptive Planning - Time Configuration, Default Time Stratum, System Setup Prerequisites.