You shouldn't be able to choose Full Release without hitting the trigger. There should be a popup telling you this and it should be impossible to submit text if you select Full Release without meeting the condition.
With respect to the thresholds, it's a bit of a mess right now. I need to figure out a way to manage the different types of conditions without the explanation being extremely verbose, but also without it being ambiguous, as you point out. For turns, if you put in 5 you need to progress 5 turns. For differences it is currently the difference in raw values.
What the threshold does is influence the narrator's decision of whether to nerf your power or not. It is prompted to assess how OP your proposed ability is against some examples of fair powers, and part of the assessment is how restrictive the condition is--more restrictive gives you a higher ceiling for the release ability.
Thanks for all the great feedback, by the way!