Run down to the other end, picking up all the constructs on the way, then AoE them down. Timed quest completes.
Head to the left (the door at the other end does not open), when you kill the first creature, new timed quest: kill all the protectors, one of each type. These are the adds/mobs, not the boss creatures.
Kill named 1 at the end of this corridor, the nameds pop sequentially, so pulling the whole zone is not possible.
Head for the far 2 corridors, turn toward the diseased skeletons, at end, kill named 2, head for the fire elementals, and now the fire protector should be present. Kill named 3.
There were two doorways locked by magic when you ran past them to gather the constructs (back toward the beginning of the zone).
One doorway is now open. Before you go down there, stand next to the closed doorway and AoE, you will be able to kill a magic protector this way without having to wait longer. Then go forward and go down the open corridor, killing named 4. (The timed quest now completes.)
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