[RPG] How does the Day/Night cycle work on the Elemental Plane of Fire

You'll be wanting the 3rd Edition Planar Handbook, whose section on the City of Brass helps flesh out the Plane of Fire as well; the 2nd Edition sourcebook The Inner Planes; and the 2nd Edition Al-Qadim sourcebook Secrets of the Lamp (if you can find it). The 2nd Edition Planescape Monstrous Compendium III offers some notes on Fire wildlife such as the waiveras and scape, but the only new indigenous creature it introduces is the fire bat (other entries such as animentals, fundamentals and ruvoka pertain more broadly to all the Elemental Planes and may or may not be of use). If you want to poke around in it, the 2nd Edition Mystara Monstrous Compendium includes the helion and pyrophor, two more unusual denizens of the plane. Finally, there is a Planescape adventure (The Eternal Boundary) that takes a spin to the plane, but overall it's nothing you wouldn't get coverage of from other sources.

You may want to ask around on Planewalker for more information or check out the work they did on their 3.5 setting conversion; it includes a section detailing the Plane of Fire.

This answer is not RAW, but RAW probably does not answer your question.

In the real world, slime mold moves, but very slowly. With regard to combat, they are functionally immobile. With regard to life cycle, it's entirely possible they could climb back up to the ceiling in a few hours.

Alternatively, it could be part of its life cycle. Green slime may need to consume an animal in order to reproduce. They collapse onto an animal, kill it, then use the abundant nutrients to form fruiting bodies. These release spores into the air, which attach to the walls and ceiling and form more green slime. The slime on the ground dies, its purpose fulfilled. You can basically think about salmon swimming upstream, spawning, then dying, except instead of a stream, it's a person.