ProgressBar1.Min := N;
ProgressBar1.Max := M;
for i := N to M do begin
  comanda;
  ProgressBar1.Position := ProgressBar1.Position + 1;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Timer1.Enabled := False;
  Timer1.Interval := 1000;
end;

procedure TForm1.BitBtn1Click(Sender: TObject);
begin
  Timer1.Enabled := true;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  if progressbar1.Position = progressbar1.Max then
    progressbar1.Position := 0
  else
    progressbar1.Position := progressbar1.Position + 1;
end;