IIRC, everything on the enemy is time based while everything on the player is turn based.
It's why for something like the water prison raid, that def buff from her overcharge just bogs things down unless someone has Chaos Magic.

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Sorry, overdrive.

So in theory, yea, you can just walk away for 3 minutes for Rahab's atk buff to expire. The downside is that you let the debuffs you placed on her to expire too.