I have a saved search that has a column based on a formula dates result. How can I add this column as a filter? I tried adding Formula(Date) as a filter but the field to select the date is read only and set to all.

I'm not sure what you mean by read only but a formula date filter can work in a saved search. However it will only filter on the first formula column in the list so set your formula date before all other formula columns in the results tab I've found it to be very buggy but can work