.Please find attached a zip file which contains a Microsft Excel worksheet that demonstrates how to generate a batch report, to csv output, and calculate a basic Mean Time to Remediation by selection only FIXED vulnerabilities and apply a formula LastDetected - First Detected.
This method demonstrated in this example can also be applied to open items, to provide "age" for an unremediated vulnerability by generating a batch report that selects NEW, ACTIVE, REOPENED vulnerabilities and apply the same formula LastDetected - First Detected.
One can expand on your formula to account for special handling for REOPENED vulnerabilities factoring in additional date parameters from those Qualys stores:
|First Detected||Last Detected|
|Date Last Fixed|
This report is meant to demonstrate the possibilities and to get your creative juices flowing.