The fields are stored as DateTime types in the database and are accessed as DateTime in the UI. There is nothing preventing you from using standard CRM fields as Date/Time values with seconds/milliseconds, etc. Of course the standard CRM DateTime
field UI will not support viewing/updating a field as such, so if you need the user to interact with the value(s) including seconds, you'll have to create an IFrame with HTML/JavaScript or Silverlight to do it. If the user does not need to interact with
the field you can manipulate the value through JavaScript alone.
-JayB