An event that only appears in the Main Chapters. You have a double chance to get treasure in certain stages during this event. This event usually lasts an hour. This happens at least once a day, either at 12:00, 17:00 or 21:00, except for Cats of the Cosmos, which doesn't have a set time for treasure festival. So, when you see Cats of the Cosmos having treasure fest, you should go and farm some treasures!
They will usually come for a single stage at a time, however, rarely all stages can have an increased treasure chance! Magic!
Sometimes, during a big celebration event, Treasure Festival will be on, celebrating the event. Every day, treasure chances will be higher in either Empire of Cats or Into the Future, alternating. Additionally, every three days, Cats of the Cosmos will also have improved treasure chances.
Here is a link to the PONOS Event Calendar where you will find daily schedules for all events that appear on a rotation in Battle Cats, including treasure festivals and event stages that appear at a particular time of day. The calendar updates every Monday and lasts through the following Sunday.
Click here to find PONOS's official Battle Cats Event Schedule Calendar.