How are we supposed to know? Only Game Freak and Nintendo know when the event goes on if any. Do remember that those Pokemon might not ever get an event; it is very possible that they were just left in the coding, never to be used at all.
If those Pokemon really are meant to exist though, there doesn't seem to be any other area that they could use. Think about it though - looking at those Pokemon, they don't seem to be the kind that live somewhere in a power plant.
