So Union Events typically happen during the first two weeks of every month (except this month because it was replaced by the collab event). They used to be called 'Sector Events' up until last year which I think was more descriptive, but basically they're events that focus on a single sector where one 4* card is the event reward (as opposed to the 3* Koga this time).

The first copy of the card is at 5,000,000 points and that's what would clear the mission, so unfortunately for any new players the first chance to clear it would be the beginning of December.