You never had to run up the stairs to get them to spawn. Just running out of the room and around the box in the area where the Sword guys spawns and back in is enough. Not sure on the timing, it's probably either about the same as jumping up and down if not perhaps a bit quicker if you're using rockets and supers at the entrance to the room. Either way not a bad spot. Has anybody tried farming the Seige of the Warmind mission? Not sure how the glimmer/sec would work out there, but lots of yellow enemies after Omnigul spawns. Might have to try it out later.