This report shows the "Response time" (time between the ticket creation and ticket's "start date") and "Resolution time" (time between ticket creation and ticket being closed) graphs.
You can set the date interval, then select the "group by" parameter that tell the system to calculate average response time per day, week or month.
As in many other reports in the helpdesk system, you can export the result to a CSV-file to open it in Excel (or any other spreadsheet) later.