Help with Dashboard prompt for Date Created

I have a combined analysis that shows new leads and opportunitys created during a cetain time period (for example the prior week).  My reporting areas are Opportunity History and Lead History.  I have the Created date column in both reports and have used the Cast(as date) formula on both to just display the date without the time.  I am trying to create a dashboard with a filter prompt where the user can put in the date created range using the calendar, but I cannot get it to work.  I know the Created date has different names , so I am