My thought would be to calculate the time difference between when the ticket was logged, and when a help desk SVD logged an action against it.
Tickets with a workflow could be a bit trickier, depending on how your workflows are set up. If you have something like an approval stage that happens before any work gets assigned to a tech, then you might need a different approach. In that case, I would go with something similar, perhaps the time difference between the first stage action taken by a technician, and the previous action.
It gets a bit further complicated if you have a scenario where a tech takes an action on a task, but doesn’t close it right away. I think to deal with that, I would maybe look at reporting on the task instead of the parent ticket.
It’s a complicated reporting scenario, and I think there is a possibility that you may need to use more than one of those techniques, setting up filters on the query to prevent tickets from being counted twice, and then union the individual queries together.