What counts as the end of Setup for “During Play” Adversary/Scenario effects? And how are they different from “After Setup” effects?

What counts as the end of Setup for “During Play” Adversary/Scenario effects? And how are they different from “After Setup” effects?

During Play effects do not affect Setup, but do affect normal gameplay. Setup normally ends with the initial Explore, with normal gameplay starting with the first Spirit Phase, but some Adversaries and Scenarios have Setup instructions that happen after the initial Explore and before the game starts.
There is no difference between During Play and After Setup effects that happen more than once. With Jagged Earth turning "after" into a key word for Triggered Actions, if "after Setup" were interpreted as strictly as possible, it would make the associated effect happen exactly once, between Setup and Spirits choosing Growth Options on the first turn. With the exception of Guard the Isle's Heart, which explicitly adds an extra step to Setup, "after Setup" effects from Jagged Earth and earlier should be interpreted as "During Play."