There's a couple of ways of doing this:
1) Base the query on the Close object. This will only show you closures but will definitely be 100% accurate within the conditions you give it. You can still get the results set to launch the incident by changing the settings on the General screen. If the incident was closed more than once in the period it will be counted for each closure.
2) Base the query on Incident and have two conditions:
AND Status in one of (Resolved, Closed)
AND Last Update is between x and y
Depending on how your process is set up and what actions are available at these statuses you should get relatively accurate results using the above conditions.
3) Use a Crystal Report.
EMEA ServiceDesk PSE
Thank you, that worked like a charm!