6:25 is when P3 starts. The way this group handles the fire and positioning of guldan is pretty good. They do not bring him to the edge of the platform. This allows them to place fire a bit more freely, because when he does his storm ability, it catches more of the room and more of the fire is removed. If we continue to tank him on the edge, we're only going to get the radius of the storm, and not the diameter if that makes sense.
They also place fire on both sides, and don't clump up which keeps more fire from spreading. On our p3 attempts we had a ton of fire all in one location - we don't need that. It was making it way more difficult to drop and people were running into each other causing more fire to drop.
Watch this video from 6:25 for 1-2 phases of Guldan's storm ability. It really simplifies the phase.