On the **Tools / Options / Calculation** menu set **Iterations** to **one**

Set up a new cell, lets say in **A1**, that is equal to itself plus 1 (yes, it is a circular reference)

Each time you calculate, by pressing key F9, you will see the value in **A1** increase by one.

Put your formula inside an **IF** statement so that the your formula only executes when the **A2** is equal to one; and is equal to itself when **A1** is not equal to one.

So for example:
Lets say your formula is in **A2** your formula would be **=If(A2=1,Today(),A2)**

You can test this for yourself using Excel's Now function formatted to show minutes and seconds.

To reset the New Cell back to one, click in the formula bar and hit enter. (ie - re-enter the formula)

This should work provided you are not using Solver elsewhere in the work book.

Also note, that if you have other circular references in the workbook, Excel will not flag them as such.