Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

uses
   ComCtrls;

 const
   DTM_SETFORMAT = $1005;

 procedure TForm1.Button1Click(Sender: TObject);
 var
   sFormat: string;
 begin
   DateTimePicker1.kind := dtkTime;

   // Don't show the seconds, Sekunden nicht anzeigen 
  SendMessage(DateTimePicker1.Handle, DTM_SETFORMAT, 0, Longint(PChar('hh:mm')));

   // To show AM/PM 
  SendMessage(DateTimePicker1.Handle, DTM_SETFORMAT, 0, Longint(PChar('hh:mm tt')));

   // 24-hour clock: Be sure to set Kind to dtkTime 
  DateTime_SetFormat(DateTimePickerTest.Handle, pChar('H:mm:ss'));

      // To show Date and Time, Datum und Zeit anzeigen 
  // Note that you can only edit the date or the time depending 
  // on the Kind (dtkTime or dtkDate). 
  SendMessage(DateTimePicker1.Handle, DTM_SETFORMAT, 0, Longint(PChar('dd/MM/yyyy hh:ss')));

   // You could also use the DateTime_SetFormat macro: 
  DateTime_SetFormat(DateTimePicker1.Handle, PChar('M/d/yyy'));

      // Instead of using the DateTime_SetFormat function, you can 
  // send a message to the control directly: 
  sFormat := 'dd-MMMM-yyyy';
   DateTimePicker1.Perform(DTM_SETFORMAT, 0, DWORD(sFormat));
 end;

 // Show the Week Number in a TDateTimePicker 

procedure DateToWeek(dtDate: TDateTime; var AWeek, AYear: Word);
 const
   FIRST_WEEKDAY: Integer = 2;
   FIRST_WEEKDATE: Integer = 4;
 var
   wMonth, wDay: Word;
 begin
   dtDate := dtDate - ((DayOfWeek(dtDate) - FIRST_WEEKDAY + 7) mod 7) + 7 - FIRST_WEEKDATE;
   DecodeDate(dtDate, AYear, wMonth, wDay);
   AWeek := (Trunc(dtDate - EncodeDate(AYear, 1, 1)) div 7) + 1;
 end;

 procedure TForm1.DateTimePicker1Change(Sender: TObject);
 var
   sFormat: string;
   wWeek, wYear: Word;
 begin
   DateToWeek(DateTimePicker1.date, wWeek, wYear);
   sFormat := 'dd/MM/yy Week:' + IntToStr(wWeek) + '';
   DateTimePicker1.Perform(DTM_SETFORMAT, 0, DWORD(sFormat));
 end;

 procedure TForm1.FormShow(Sender: TObject);
 begin
   DateTimePicker1Change(Self);
 end;