Erro Expression Evaluation not supported.... Somando horas

with QryHoras do
    begin
      close;
      sql.Clear;
      sql.Add(´Select Aluno, Sum((HorarioInicial + HorarioFinal)) AS HorasMarcadas From Teoricas´
              +´ where Aluno = :Alu Group By Aluno Order By Aluno´);
      ParamByName(´Alu´).AsString := TxtCod.Text;
      open;
    end;

   Total :=  QryHoras.FieldByName(´HorasMarcadas´).AsInteger;
   Horas :=  Total / 86400;
   Edit1.Text := TimeToStr(Horas);