Ref DateTimePicker:
The ooDialog reference (7636) says, of the SHORT and TIME styles:

    The format displays like: 6/22/11.
    The format displays like: 5:31:42 PM.

On my system (in the UK), they display like this:
Looks like the Windows locale is getting a look in (which is good).
Maybe add text to say (e.g.), "The precise format of time and date for SHORT and TIME will depend on the locale. The formats shown above are true for the USA."