When are external vault users and groups synchronized by default?

 By default, external vault users and groups are synchronized once every 24 hours between 1 AM and 5 AM. This synchronization schedule is determined by the AutoSyncExternalObjects parameter in the DBParm.ini file, which specifies that the Vault’s external users and groups will be synchronized with the External Directory during this time frame1.

References:

CyberArk Docs - Synchronize External Users and Groups in the Vault with the External Directory