Avoid image blinking when timer is used

I have a background image in my application, but it gives the impression of blinking due to the use of Ttimer that the application has.

I tried to change the interval of Ttimer but the problem persists.

Any tips on how to solve?

Timer code:

procedure TfrmPrincipal.Timer1Timer(Sender: TObject);
begin

if ( TimeToStr(time) < '05:00:00' ) or ( TimeToStr(time) > '24:00:00' ) then Application.Terminate;

    if (timetostr(time) >= '23:50:00') and (timetostr(time) <= '24:00:00') then
    begin
    Timer1.Enabled := false;
    if frmmodulo.qrcaixa_operador.FIELDBYNAME('situacao').AsInteger = 1 then
    begin
    application.messagebox(Pchar('Já são ' + timetostr(time) +
    ' e o Caixa do dia ' + datetostr(frmmodulo.qrcaixa_operador.FIELDBYNAME
    ('data').asdatetime) + #13 + 'Ainda não foi fechado! Verifique!'),
    'Atenção', mb_ok + mb_iconwarning);
    end;
    Timer1.Enabled := true;
    end;

end;