Exactly 48 hours before the start of a community adventure, the beta server will be notified.
Inno-Games is really a shame in terms of customer friendliness :-(
Btw, the icon for the FA appeared much later than usual. Before we had 3 or 4 days ahead (don't remember exactly) but definitely not only 48h.
Now are less than 48h, I missed the right time to start 2 days production and to be ready when the FA starts.
It seems like it is an intended new setting by Innogames. We were getting the in-game countdown banner 3 days before the events start, but now we are only receiving it 48 hours in advance. It also happened with Mama Juul event on live servers.