I've had events where I got both drops within the first day or two. (Quite a few like that, actually.) Sometimes one takes a bit longer to drop but it seems like that's still within the first half of the event's duration. So far in this current one Bunny's Mom has been refusing to drop for me though. I'm thinking this might end up being Festival Bonny all over again. (I spammed the fight for her in that event who knows how many times a day every day all the way to the end with no luck.)
Only one new girl per month (not counting event drops)? Even with the help of whatever hidden bonus we're getting on future rolls from failure streaks? That sounds slower than it seems like has actually been the case...