unit DateTimePicker.Interposer;
 
interface
 
uses
  System.Classes,
  System.SysUtils,
  Vcl.StdCtrls,
  Vcl.ComCtrls,
  Winapi.Messages;
 
type
  TDateTimePicker = class(Vcl.ComCtrls.TDateTimePicker)
  protected
    procedure Change; override;
  private
    FMoveCursor: Boolean;
    procedure WMKeyDown(var Message: TWMKeyDown); message WM_KEYDOWN;
  end;
 
implementation
 
{ TDateTimePicker }
 
procedure TDateTimePicker.Change;
const
  CDtSep = '/';
var
  FEdit: TCustomEdit;
begin
  inherited;
  if not DroppedDown then
    if DateFormat = dfShort then
      if Format.Contains(CDtSep) then
        if FMoveCursor then
        begin
          FEdit := TCustomEdit(Self);
          if Trim(FEdit.Text)[FEdit.SelStart + 2] = CDtSep then
            Self.Perform($0100, $27, 0);
        end;
end;
 
procedure TDateTimePicker.WMKeyDown(var Message: TWMKeyDown);
begin
  if not DoKeyDown(Message) then
    inherited;
  UpdateUIState(Message.CharCode);
  FMoveCursor := Message.CharCode in [96 .. 105];
end;
 
end.

unit Unit1;
 
interface
 
uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ComCtrls, 
  JvDateTimePicker, Vcl.StdCtrls, Vcl.Mask, DateTimePicker.Interposer;
 
type
  TForm1 = class(TForm)
    DateTimePicker1: TDateTimePicker;
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
end.