You'll need a field in the cube (it could be a calculated member) that is a date (e.g. "01/01/2013"). If you know your MDX, you could created a calculated member in Tableau from the existing fields. Don't be surprised if a date field in the cube comes through as an attribute instead of date (just right click it and select "Change Data Type" --> "Date".)
Thanks Joshua. Is there any ways I can make the date hierarchy as date instead?
Also I know how to create a calculated members but for some reason it ended up in the measure group. how do you create a date calculated member under the date dimension?
I just added this comment to your other thread on the same subject.
I have been writing a couple of articles on designing, building and using cubes with Tableau.
You can read the article here:
Hope that it helps you