Filter a CQWP on time portion of datetime field

I'm using the content query web part to show news items on our Intranet's home page.  I can filter on a datetime field to show all items from  [Today] and older and that works great.  I need to also filter on the TIME part of that datetime field/column so that I can add items to my list that should only show up at a specified time of the day.  You know, items that are under embargo until a certain date and time.

I tried to filter by [Now] but SharePoint does not recognize that filter option.

Any help would be much appreciated.

Thanks!

Rick Jenkins