i think they were confirmed to be 2.5 times the normal rate for SSR Eidolons in one of the guides...
while banner kami will eventually get 15 times the normal rate at some point
i thought the last one happened around april... if they're every 3 months, wouldn't that make it july for the next?
EDIT: had to backpedal here cause i realized the first was around christmas so it's 4 months gap, not 3