unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, StdCtrls;

type
  TForm1 = class(TForm)
    Timer1: TTimer;
    Label1: TLabel;
    procedure FormKeyPress(Sender: TObject; var Key: Char);
    procedure FormCreate(Sender: TObject);
    procedure FormShow(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

var
  n: byte;
  StartTime: TDateTime;

procedure TForm1.FormKeyPress(Sender: TObject; var Key: Char);
begin
  inc(n);
  case n of
    1:
      begin
        Timer1.Enabled := True;
        StartTime := Now;
      end;
    2: Timer1.Enabled := False;
    3: Halt;
  end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  DoubleBuffered := true;
  n := 0;
end;

procedure TForm1.FormShow(Sender: TObject);
begin
  Label1.Left := (form1.Width - Label1.Width) div 2;    //не выполняется
  Label1.Top := (form1.Height - Label1.Height) div 2; //выполняется
end;

procedure TForm1.Timer1Timer(Sender: TObject);
var s: string;
begin
   DateTimeToString(s , 'hh:mm:ss.zzz', Now-StartTime);
   Label1.Caption := s;
end;

end.