In the second Trial, two teams were disqualified, which is to be expected since there were only ten numbered doors. The third trial, however, didn't force any team out of the competition, at least not in the normal way, per se.
Hypothetically, all teams could possibly complete the trial by either surviving for five minutes or defeating the summoned monsters. Unfortunately, some teams were unlucky enough to face a monster that counters them, or more precisely, their techniques and ability, like what happened with Isadore's team, for example.
As Gutcha had previously said, each time was to fight for five minutes, or less if the monster defeats the youngsters. A ten minutes-long break was to be held after each fight, so, in total, the trial took exactly 133 minutes. Out of the ten participating teams, two more were disqualified, leaving only eight.