I am not sure if this can be done but here is what I am looking for help with

I have 2 columns in a spreadsheet that I use to record the date and time
that a machine breaks and the date and time that is repaired.

Right now the cell formating is mm/dd/yy hh:mm AM/PM -
I added a column that calculates how may minuts/hours/days the machine was
down.
I was wondering if I could change the cell formating that shows not only
mm/dd/yy hh:mm AM/PM but also shows the Day of the Week (Mon, Tues, Wed).

What I am trying to do is be able to deduct weekend hours from my two
columns - So if my machine goes down on Thursday and is back working on
Tuesday, I can calculate only how many business hours it was down

Any ideas??
Kim