The automated Purge job can only purge events which are older than 1 week
Some customers may want to purge events from their production database that are younger than 1 week old. Currently, this is not possible, as the earliest event that can be purged is one week old.
This behavior is currently by design.
Enhancement request (TF00394466) has been submitted, but Product team have confirmed that this will not be fixed in any future version.
In document Change Auditor User Guide, at page 116, it is documented that the purge all events older than option consists of calendar Day(s). Document defect (TF00414447) has been logged to improve on the document.