An alliance killing each spawn as soon as it appears can kill roughly 80 Ebony Pudding over the course of 1 Fire Day. So, expect to take at least 3 instances of Fire Day to finish this trial.
As a Blue Mage with 10/tick refresh from atma, I was able to kill the Licorice in Abyssea - Konschtat (near conflux 6) much more efficiently than Mount Zhayolm. There is a lotto NM there but it does not aggro or link with the other Flans (just take care when using AoE). These Flan don't aggro job abilities.