The event details say, "You can clear Asula's Den only one time during 12:00-22:00 (10 hours) Server Time."
So how did it start at 12:00 and disappear at 14:00...it should still be available for 8 more hours according to the Event Details.
How many other people missed this because they read the Details and just like other events that had these same Event Detail schedules...assumed 10 hours meant 10 hours and not 2.