I have two custom fields that indicate shipping windows for items being returned to clients inside an SLA. I want to create an alert (email) to a supervisor on the day of the these dates.

It doesn't look like we can do this with Workflow but perhaps with Supervise however when I select the custom field in the criteria, I get a calendar control to set the value unlike if I select Due Date where I can execute off CurrentTime.

Is there a work around or better solution?