Is it cheating if you sit in a world a wait for it to become night to make easier to lavas pools since the timer for your run doesn’t start till you move? I don’t think it’s something I’ll ever do just a little shower type thought and was really curious. Because according to the rules I don’t think it should but I don’t know.

No that would not be allowed as it is classified as an advantage for certain categories. Timing Rules

• Timing starts on the first frame of movement after world creation
• You may wait for a reasonable amount of time at the start of your run for the world to load
• During this time you may not move, but you may pause so that the world may load
• For cooperative runs, neither player may move during the the grace period

Plus it would be unfair on the mods to have to watch a still screen for 11minutes before the run actually starts

It also isn't worth your time. You could spend that time resetting for a lava pool instead of just making it easier to find one.

I understand the shower part, but as @MangoBo1 said above me it is a huge waste of time and you would more then likely be killed by a mob at night anyway.