The Audit interval is by default 'Daily' (24 hours from the last audit time for the device). You can change the interval to hourly or two from AMP Setup > General. However, this is global setting and would take affect for all devices and can cause perfromance issues if there are lots of devices.
Regarding the query about the change of config, is that done from Airwave? If so audit should happen immediately. If the config change is done on the device, then the audit will happen based on the interval.