The system log shows that the PAN-DB version is updated approximately every 5 minutes.
Details
Every 5 to 10 minutes a new version is published, which contains updated categorization data and an incremented version number. Each time the Palo Alto Networks firewall sends a request to the cloud it checks the current version number. If it is different it upgrades the device’s version to the current cloud version.
The updates are this frequent primarily to leverage native integration with WildFire which creates new signatures and records malicious URLs every 5 minutes