Using Sqlserver 2005 beta of a relational table in Oracle 9i.

The table contains date/time fields with resolution down to hour.
There's no time hierarchy in the database, so I wanted to use the
Server Time Dimension facility of AS. I can make a cube fine using a
Server Time Dimension if the date/time fields contain only exact days,
but how can I add knowledge of hours into its hierarchy?

I'm a newbie so sorry if this is a silly question.