Rising Event

[Squintina]

Picture of the message from the french client :

Well technically if I translated that first sentence word for word.

Diverse exercises are organized in a random manner throughout the entirety of the Commemoration Party (Rising Event).
So while it's possible that it might mean that the NPC comes up randomly. I personally think what it actually is trying to say is that the fates inside the instance (which are the exercises, or "maoeuvres") will be popping at random.

It's probably just an intentional delay to get more time zones on the 27th, the date of ARR's release.