Business Hours elapsed time_diff function

rather than using the time-diff() function, we would like to create custom reports showing elapsed time in business hours - it would be helpful (rather than writing this ourselves) if you could provide a bushrs_time_diff() function for use in the reporting tool that looks up local business hours based on site of a ticket then calculates the elapsed times between notable events for reporting purposes

going one further it would be nice if the elapsed business hours were simply a field somewhere

so we have the very useful

created to response
created to assigned
assigned to responded (may be negative right now, this begs another feature, state/event based mandatories)
response to completed
created to completed (I think this one exists as total time on ticket..which is somewhat misleading as it is duration not effort)

/kdl