Create Excel Condition involving Name of Day

Registration date
Monday May 19, 2014
Last seen
May 19, 2014
How to create a formula, if the value falls on say Saturday, the value must step back for a day say Friday???

Our inspection date should fall on working days and the requested date should also fall during working days....

I want that the requested date should be a day before the inspection date.

Our day off is on Friday so that means If my

Formula A1=B1-1
Where B1= Date of Saturday
A1=Become Friday
I want a formula where if ever it happens that way, my formula becomes A1=B1-2

I tried this =IF(A1-1="Friday",A1-2,A1-1) but not working...
Any help?