Setting the policy specifies the period in milliseconds at which the device management service is queried for device policy information. Valid values range from 1,800,000 (30 minutes) to 86,400,000 (1 day). Values outside this range will be clamped to the respective boundary.
Leaving the policy unset means Google ChromeOS uses the default value of 3 hours.
Note: Policy notifications force a refresh when the policy changes, making frequent refreshes unnecessary. So, if the platform supports these notifications, the refresh delay is 24 hours (ignoring defaults and the value of this policy).