Office Hours for ticketing reporting

We are having trouble with office hours not being taking into account for the ticketing reporting. 

For example, the report says the ticket was open for 1 day and 4 hours

When you look at the breakdown on the ticket it says:
ticket open: 22/05 at 1:36PM
ticket closed: 27/05 at 4:52PM

There is more than 1 day and 4 hours between those dates. If you convert the 1d 4hrs into 24 hour time you get 28 hours, then divide by 8 you get 3.5 working days which is correct but it is not displayed correctly. 

Does anyone have a work around for this? 

Thank you!!