I was wondering if anyone knows the respawn periods of loot, items/junk, enemies, cleared areas etc and if some areas are different than what those are and whats the respawn time. I mainly interested for the aluminum currently in the Mahkra fish packing plant. I've read 3 days, 30 days, 2 weeks etc for different things.

As far as Mahkra I waited in that chair right in front of the ammo box sitting on the conveyer belt where the trays are. Do i need to be out of the building entirely for them to respawn? Do all the enemies in the building need to be dead first? Because I killed them all and went outside a few times after waiting (in chair) for 2 weeks (too late & sleepy in real life to wait a month, will try again today), still nothing.

Just wondering what the rules are and respawn times on the main things like loot, items/junk, enemies, cleared areas etc. I have the Vault Dwellers Guide but that doesn't seem to mention much about respawn rates just that things will respawn.

The cell won't reset while you're in it, you need to leave and stay out for a while (I usually see 3-7 game days, though some resets have taken up to 2 weeks in game).