Calculate a duration in business hours, ignoring week-end and possibly certain bank holidays.

I want to calculate the number of BUSINESS hours between two timestamps over a week-end, how do I achieve this thru reporting and/or expression builder?

Details:

Business hours are from 9am to 6pm (so 9 hours per working day)

Activity starts on Friday at 4pm and ends on Monday at 10am

Based on the above the duration should be 3 business hours and not 66 hours...

To make it even more realistic, how do I also ignore bank holidays?

The example from Mike Lairson book does not go to this level of granularity (hours and not days)