Displaying duration values - MDX expressions in FORMAT_STRING

Suppose you have a calculation (or even a real measure) which returns elapsed time or duration. We want to present it to the user as such, i.e. break into hours, minutes and seconds. This sounds easy enough, we would just use appropriate FORMAT_STRING. If we read documentation, we quickly find that by using ‘hh’ for hours, ‘mm’ for minutes and ‘ss’ for seconds, we can have ‘hh:mm:ss’ formatting, i.e.