I would just be more descriptive about what the date is... if it's a "time stamp" of some sort, then I think that's descriptive... I'm suspecting that it's a CreatedDate or ModifiedDate of some sort, in which case I would simlply say that: "Date Created" or "Date Modified"...
The fact that it includes the time doesn't need to be reflected in the column header...
EDIT
After evolving through this thought, many of us agree that the word date is not even necessary "Created", "Modified", "Ordered", etc.. is what I feel is the most concise way to do this. The fact that it's a datetime should be inferrable in most instances.