Thank you. I don't know how I overlooked the quotes in the documentation. Regarding the WHERE statement, both versions work. I don't know if one is better.
Yes I get the same query results if I use <> null
It's been a few years, so hopefully you're using "is not null" instead of "<> null" by now. Reference: How to Get NULLs Horribly Wrong
Thanks. I didn't know about HOUR. I'm not sure whether to select your answer or Icarus. Both get the job done. I'll leave the question open for a bit to see of the votes indicate whether one approach is better.
DatePart("h", "01/05/2012 9:54 PM") returns 21 and not 9.