unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
    procedure MyOnTimer(Sender: TObject);
  public
    { Public declarations }
  end;



var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.MyOnTimer(Sender: TObject);
begin
  (Sender as TTimer).Enabled := False;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  Timer: TTimer;
begin
  Timer := TTimer.Create(Self);
  Timer.OnTimer := MyOnTimer;
  ... 
end;

end.