Calculate Difference between two Date/Time

I am currently usins Excel 2007 and would like to calculate the diferrence in hours and minutes (ideally in decimal e.g 4:30 should be reflected as 4.5) between two date and time groups, excluding the non-working time between 17:00 and 09:00, weekends and holidays. An 8 hour working day is to be used.

I have attached a spreadsheet were I tried to achieved the above with little success. Your assistance will be greatly appreciated.

Using your file

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assumes start/end will never fall on non-workday ... if they do you will need an alternative.

the above formula is c/o daddylonglegs