The issue is that you are trying to compare the value of a field with itself. So it will always be equal to itself.
So you need to capture the value of the field in a separate field.
I have not tested this, but try a setting up a field called [Old Actual Est Date (concept)].
Have a form rule that says
When the record is saved, change the value of [Old Actual Est Date (concept)]. to the value in the field [Actual Est Date (concept)]. That way you will have the old value to compare to.
You should initialize the value of [Old Actual Est Date (concept)] to the on that field to the current value on the field [Actual Est Date (concept)].
You can either do that with copy and paste in grid edit if there are not too many records or else make that field a formula field equal to [Actual Est Date (concept)] and then change he field type back to a date field. It will retain its calculated value.
