How to get total business time as Resolution Time

Hi All, 

I need to generate a report that shows the case resolution time and includes business times and days, not the total time.

So far, I have created an SSRS report which retrieves the ActualEnd field from the Case-Resolution entity (Activities) and using the CreatedOn field from the Case entity. However, my clients do not like this report as it does not have the real business time resolution. They want to see a report which includes only business time. 

Do you have any ideas how to achieve this?

I have noticed the Actual Start field is not populated on the Case Resolution entity and therefore neither the ActualDurationMinutes. Could you please advise why this field is not systematically populated as the Actual End field?