All mini-events start and end at 8:00 a.m. local time, except for the last mini-event, which ends at 12:00 a.m. together with an Event. The only exceptions are the Detective Contest and Order's Chest mini-events. These two events start simultaneously for all players according to their own special schedule. These mini-events become unavailable when they end, even if you change the date or time on your device.