After the defeat of mother brain you have to do an emergency evacuation due to a time bomb. The platforms are tiny but repeat in the same format. You need the high jump from Norfair fire zone. Jump to the top platform first then next to the wall then up. Step down and hip the lower one from your current platform jump up and to the wall. Repeat this process carfully and you will make it out with about 500 ticks of the clock left.
The mother brain can be hard to defeat. It beats faster as it weakens and restores if you stop hitting it like a Zebite. A great tip is to use the screw attack and rip through the fire rings while staying up by mother brain and shooting it consistantly. Seperate hint for evacuation next