Filled Requisition Date

Summary

How can I change the format of my newly create field to be a 'Date' field, that then allows me to be able to prompt on Dates Between in the front page filters.

Content

I had a request to add the date when the Requisition became 'Filled' on one of our OTBI reports.

I used the following formula to bring back this date.

MAX(CASE WHEN "Job Requisition History - Event Details"."State Code" = 'REQUISITION_FILLED' THEN  "Job Requisition History - Event Details"."Event Date"  ELSE NUll END)

This seems to work, except that my new field is a 'measure' attribute and I need it to be a 'date' attribute' to allow the end user to be able to use the filters on the front end for the filled date is between...