About grand boss event. If there's Baium, I think you should increase event time, I know that you have already increased it, but now, when population in server is quite low, there's not enough ppl to kill Baium in ~10-12 mins (3-5 mins fighting against other team), because usually wins party with tanks/bishops and damage dealers are like 2 mages and 2 archers, impossible.
There will be maximum healers count restriction in grand boss challenge event after next restart.
Time to kill baium will not be changed at least in near future.