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 TAutoCloseForm = class(TThread)
  private
    procedure UpdateCounter; virtual;
  protected
    procedure Execute; override;
  public
    AutoCloseTime: TDateTime;
    constructor Create(CloseTime: TDateTime);
  end;
.
.
.
constructor TAutoCloseForm.Create;
begin
  Inherited Create(true);
  Priority:= tpIdle;
  Resume;
  AutoCloseTime:=CloseTime;
end;

procedure TAutoCloseForm.Execute;
begin
  while not terminated do
    Synchronize(UpdateCounter);
end;

procedure TAutoCloseForm.UpdateCounter;
begin
 if Now=AutoCloseTime then begin
  Terminate;
  //Close;
 end;
end;                    

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Form1.Close;
Form1.Terminate;
MainForm.Close;
etc ...                    

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  TAutoCloseForm = class(TThread)
  protected
    procedure Execute; override;
  public
    CloseForm    : TForm;
    AutoCloseTime: TDateTime;
    constructor Create(Form : TForm; CloseTime: TDateTime);
  end;

var
  Form1 : TForm1;
  Thrd  : TAutoCloseForm;

implementation
{$R *.dfm}

constructor TAutoCloseForm.Create(Form : TForm; CloseTime: TDateTime);
begin
  Inherited Create(true);
  AutoCloseTime:=CloseTime;
  CloseForm:=Form;
  Resume;
end;

procedure TAutoCloseForm.Execute;
begin
  while Now<AutoCloseTime do Sleep(0);
  PostMessage(CloseForm.Handle,WM_CLOSE,0,0);
  FreeOnTerminate:=True;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Thrd:=TAutoCloseForm.Create(Form1,Now+1/24/60/6); //Now+10sec
end;