I have a habit of storing datetime in a text format, as it seems every database and computer platform has a different binary datetime format, and some (INFO) don't support time. When you need to do a query, or a date time calculation, you can do it easily if it is in string format, no matter where you are doing it. Also, the datetime won't get scrambled when you copy the table to a format that stores it differently (for example Oracle to .dbf).
I agree you should not separate date and time, whether you go with a binary or text format.