The moment it fires, so you can have the options be based on what happens in the immediate (using IFs and such in there can give good results).Quick question - what exactly is the point of immediate? If it is used, does that basically mean the effects within immediate are executed before the event even fires, or does it mean the effect will happen the moment the event fires?
It can also be important for multiplayer, as there events don't pause the game. So if there's something that should happen instantly when the event triggers, use immediate.