For the sorting of the column to work, it needs:
– a column header
– to have a value specified
– to be the only column sorting on that attribute
– preferably not have any null values in that column.
An existing example to look at would be the “Name” column on the EntityNavigatorPortlet.
For your case, it would require adding a “value” to the column and ensuring there isn’t another column sorting by the same “createTime” attribute.