Out of the four days of wall buffer they had expected to have after the Shadow Dragon battle, a little over three and a half remained on the counter.
Factoring in the new shadow-boosted drilling speed, that buffer translated to slightly less than sixty hours of real time. It was a tight window, yet it remained sufficient, since it gave them enough breathing room to finish resting, top off their cores, and execute a decisive joint strike against the Light Guardian before the prison gave way.
Furthermore, hunting the final guardian first could offer a massive compounding reward.
Defeating the Light Dragons would put the seventh elemental cores into Ren's hands. If he returned to this place holding all seven elements, the mana-system agony of waking Mooshito and risking further crystallization would actually be worth the price.
