From what I can tell ALL debuff protection buffs will last permanently throughout the entire fight until you get hit by a debuff.
Meaning if you have enough turns, you can apply two shields back to back immediately if one is used up from blocking the first set of debuffs. (Note: You can't have more than one shield because they won't stack.)
This is what alot of people did back in Medusa Advent. The only downside to this is that you can't block more than one set of debuff at a time. Meaning Ult Yata's burn+heal nullify debuff will only make you block one, instead of both.
A similar defensive buff ability is Oliver's "Refined tactics" or Urania's "Divination" which will last permanently until you take damage once.
Or count on the plat chest drops. That is always a possibility if you have crazy luck.