Red Kihunter Shaft
|Amphitheatre||Adjacent rooms||Lower Norfair Fireflea Room
Red Kihunter Shaft Save Room
On the way to Ridley, the earliest you can lay the last power bomb is when the blue line in the screenshot reaches the left edge of the screen as you're moving right. Any earlier and the yellow door will not open.
If you use a Power Bomb on the way out to destroy the bomb blocks, the earliest you can lay it is just before the right edge of the screen hits the middle of the door to Wasteland.
With Hi-Jump Boots, you can downgrab the top ledge. Jumping through the door transition fixes it and allows you to get to the platform in the next room quicker, but if you jump late enough to just be starting the spin jump during the door transition, that will add processing lag.
At the start of the room, the fastest way down is to fire an angle-down shot as soon as you enter, then fall into the hole and downback through the hidden section.
With Plasma, you can "hitbox" through the Kihunters by hitting them with a shot as you run through them. You can also use two charge shots (or one double-hit) to kill them, which reduces lag when the Power Bomb goes off.
It is possible to clear two of the three bomb blocks at the bottom of the shaft with a Bomb Spread from the ledge just to the left. This is necessary if you used Power Bombs in the Pillar Room, because you will need one more in Wasteland to avoid picking up the "Power Bombs of Shame".
You can use a shinespark to kill two of the Kihunters, reducing lag in a similar manner to the KPDR strat listed above, and making it so you only need to avoid one of them.
Note that the shinespark in this video is about as late as you can possibly activate it and still kill the Kihunters. With more efficient movement that window will be easier to hit.