Eric O. LEBIGOT
No instructions are followed when the triggered ability goes on the stack, it goes on word for word. The instructions are followed exactly at the time it resolves.
But the interesting thing to remember is the word "Choose" is followed during resolution, so technically the "choice" does not need to be made until it resolves which could make a big difference.)I'm not sure I'm getting this; in fact, "modal" spells require choices to be made upon casting (not resolving):
700.2. A spell or ability is modal if it has two or more options preceded by "Choose one --," "Choose two --," "Choose one or both --," or "[a specified player] chooses one --." Each of those options is a mode.
700.2a. The controller of a modal spell or activated ability chooses the mode(s) as part of casting that spell or activating that ability. (…)