How much time passes between requesting a scan for a private host and the actual start of the scan?
Scan jobs for scanner appliances are stored at the QualysGuard Security Operations Center (SOC) until the scanner appliance contacts it and polls for new scan jobs to download and execute.
The default polling interval is 180 seconds (3 minutes).
The scan will start anywhere from a few seconds to the full amount of the polling interval after it is requested.
Qualys Support KnowledgeBase