My Excel 2010 spreadsheet is a live spreadsheet exported from SharePoint. It tracks user requests which can come in at any time/day.

I have two columns - Created and Completed that I need to understand the difference between the date/time the request is created to when its completed.

Example:
Column Header - "Created" - 5/7/2012 10:07
Column Header - "Completed" - 5/7/2012 12:25

Its in military time.

I need to find the difference between the two times, taking into account holidays and weekends. The requests can come into the system at any point of time however (night /day/holidays/etc)

Your guidance is very much appreciated!