I don't think Ti'an is all that hard except for the main tank. It's harder than the crap fights in T4 like Basilisk and Imp for sure, but I don't think it's nearly as hard as Yah Chieng. Although not part of the time trial, the Ti'an priestess encounter is about as boring as anything in the game and the only challenge comes from the fact that half the group usually takes a ninja AFK at that point.