Timed (monster kills) Zana daily in Necropolis virtually impossible

I'm noticing that whenever Zana gives me a 40 second time limit (kill monsters to get more time) Kill the Boss mission in a Necropolis map the quest becomes impossible, due to a seemingly drastically lower amount of time gained per kill. It is wholly impossible to actually clear things fast enough (unless you can kill both forms of the boss in under 30 seconds, which requires stupidly high DPS, especially since she spends several seconds transitioning). I had a level 76 crit reaver in a 70 necropolis map, who was one-shotting (and shattering) whites like no tomorrow with a movement speed flask active constantly, and I could not get the timer over 40 seconds. In any other map with this mission and time limit I can fairly easily get several minutes on the timer. Not here. Wiping out an entire pack of whites with a single attack only gives me enough time back to cover the time I spent attacking, and magic and rare mobs barely give enough to get to the next pack. I've had other characters, going back to 1.3, including a level 90 crit tornado shot ranger and a level 90 barrage CoC witch that have had the same issue: they get this mission, in this map, and it is simply impossible to gain enough time to actually kill the boss, despite their incredibly high clear speed. Any other map with this mission and it's a cakewalk for them (including the reaver), as kills seem to generate significantly higher time gains in every other map.