I just did this and want to warn about how long this one can take. I started this trial at 5:30am, and finished it at 10:15pm that night. First 2 pops took almost 8 hours, and thankfully the 3rd only took 1.5 hours. Be prepared for this one to take a while, but stick with it and press on. The next trial after this killing Seww took under 5 hours to finish all 4 kills!
I suggest coming /THF and between spawns go over to other side of map and farm Water IV (expensive scroll) off Sapphire while you wait. Also I can confirm this NM will take up to 8 hours to spawn. 2/3 at time of this post. First one I was lucky and it spawned after first placeholders, second took 8 hours.
I didn't experience anything like this camping the NM. Either the person who wrote this was killing the wrong Quadavs, or he just got really unlucky. Never took more than 60-90 mins after the window opened to spawn for me.
I got all 3 in under 5 hours. All 3 times, he popped instead of the Quad furthest to the West even though the Wiki for this NM said there were 2 placeholders.