"Fun" fact: I did Sastasha with my main THM (I think on Friday), thus a DPS and I waited about 2h. Same for the next dungeons. I raised a healer to level 15 and yesterday as soon as I registered the window to start the quest appeared.

Apparently there must not be many healers around. Which is a shame, because they are the most fun to watch the battles in the dungeons in first person view while healing!!