We have a problem to get proper SLA statistics for our Incidents in SD+ and Analytics

The process

We register a ticket (status open), assign a SLA (5 working days 9 hour per day)  and work on the ticket until we can resolve it (status resolved)

Some of the tickets are set in status pending (that are OK).

The time the ticket is in status pending shall not be included in the calculated time to resolve.

Example:

SLA 8am to 5pm every work day ( 9 hours)

Ticket created day 1 at 8am

Ticket set in status pending day 2 8am

Ticket set in status open day 3 8am

Ticket resolved day 4 8am

Calculation: 

Day 1 open = 9 hours

Day 2 pending = 9 hours

Day 3 open = 9 hours

Day 4 resolved = 0 hours

The time I want to get: 18 hours time to complete

When I look in the report it seems that it calculates 27 hours (i.e include the 9 hours in pending)

How shall I configure the report to get the time correct?