The Last Updated At field is a reference field for all entities. It refers to the last time a change was made to the entity.
The date formats supported are:
dd Month yyy e.g. 24 October 2011 and 24 Oct 2011
dd/mm/yy e.g 24/10/2011
yyyy/mm/dd e.g 2011/10/24
To find all items that were last updated between 2 dates:
LastUpdatedAt >= "2011-10-24" AND LastUpdatedAt <= "2011-11-02"