Apparently Ayaka's banner was set to last 240 days, but it seems like they changed it to "before version 2.6 ends" which is still rather vague. Still funny though.
The devs are really showing how inflexible they are. They could've done any other banner, be it someone linked to the festival (which in hindsight they should've probably extended) like Albedo, Klee, Kazuha, Yoimiya or even a Mona/Jean/whatever banner to keep things fresh. But no, we're just going to extend the same banner for several weeks. No reruns of previous events, seemingly no compensation, nothing. Just weak.