This is all speculation, but I do believe there may be a couple of instances where cutscenes and timing of the effect can cause the effects fall off assuming the timing is ~15 seconds. The current one that pops into my mind is Eden's Verse: Refulgence and its savage-tier counterpart. Funnily enough, the timing of the remaining buff timer and Time Dilation may be too spread apart if it can't be used again right before and after cutscene. These instances should be few and far in between though... I think?
That sounds like an interesting concept. Relativity of a time - essentially a multi-layered compressed barrier effect reduces/changes the speed at which an attack lands, breaking it into multiple chunks before it goes through the "barrier" and reaches you. It's basically extreme time dilation within the isolated barrier happening at different levels it acts as if it's slowed down when it hits us. That, or the barrier acts using a gravitational time dilation effect.
By slowing down the damage in the form of a DoT, how will that transition when multiple hits increase? Assuming there is a skill or status effect that mitigates incoming damage but spread it out over a DoT - Will the DoT just get stronger, will it lengthen, will all the incoming damage be transferred over the remaining duration of the skill's time period, or will it create a separate DoT per attack? There is a possibility that a DoT tick being too strong due to an Akh Morn-type of attack will inevitably kill a character from accumulating too much damage if DoT just gets stronger in the period it was used, so depending on the type of burst - long duration burst periods could also be too much (though this should be highly unlikely). There is also the possibility that too much mitigation meant the need for 2 healers in a raid doesn't feel needed. Mitigating a certain amount of damage based on healer's potency itself per tick could be a solution, like GCD buff damage but on the enemy's damage instead. Can't say if it would actually work in practice or if it will be too powerful though.
The bigger question is - how will Nocturnal Sect work in relative response to this? Shields are naturally more inefficient than healing regen. The duration increase on a shield doesn't refresh the power of a shield either. I don't think the idea of shields will be removed entirely because of how the AST's SB storyline goes, but mitigation with the current AST's Nocturnal sect doesn't seem to work well once you take into account of the effects of DoTs on a Nocturnal sect shield. The eHP aspect of the shield will be whittled away by continuous DoTs first. As a result, this time delay will make Diurnal sect always more beneficial due to regens.