Thank you. You're right. I don't trust it either. The sensation intensified up to a point, beginning several days after I first arrived, but it seems to have reached a plateau. I'll continue to monitor it.

Yes, that's not an experiment that should be performed on anyone. [She frowns, briefly.]

I would say up to twenty minutes, or maybe a little more, although it's impossible to be precise with such items. If your primary goal is to escape danger, then I'm sure the barrier would last for the time it took you to flee. I don't use these; I use Materia, but I know it would take a lengthier battle to dispel their protection.