In ordinary proceedings on the merits, the cassation term is three months from the day of the judgment. But the cassation term in summary proceedings is shorter, namely only eight weeks. And in some special cases, the term is even more limited.
Obviously, a cassation opinion should not be issued only just before the expiry of the cassation period. There should be enough time left for seeking a second or even third opinion. This is another reason not to submit a case for an opinion only shortly before the deadline expires.