I'm not sure whether you are trying to figure out DN or ACD talk times. My understanding is DN Talk Time is defined as when an agent uses their personal line (In or Out), whereas ACD Talk Time is when the call is answered from a skillset queue (In Only).
If you want to calculate talk time by skillset, this can be done using the agent by skillset performance report or a customization of this type of report using something like Crystal Reports.
If you are looking for DN Talk time try using the agent DN performance report which gives you DN In and DN Out statistics per agent. Be aware that there are some differences between when a DN call is counted within the talk time as DN Out External calls add all time from when the call was initiated and DN Out Internal calls only count when the call actually connects to another agent.
All of this information is available in the Historical Reporting & Data Dictionary pdf that comes with Symposium.
Hope this is useful,
JanelleP