| No one knows who or what Zot is: demon, god, wizard, something else entirely? But adventurers seeking the Orb will, in turn, be hunted by Zot, and if it finds them, their existence will end.
Zot is very slow moving, and can only sense adventurers once they've spent an inordinately long time in one area of the dungeon. Even once this happens, adventurers will have plenty of warning to either descend to new depths in the area (diffusing Zot's attention once more) or to leave the area entirely.
The Abyss is beyond Zot's comprehension, and adventurers there are safe from it (albeit subject to many other hazards). The Hells, along with their Vestibule, are a single area as far as Zot is concerned. Adventurers who hold the Orb of Zot are forever immune to Zot's power.
Zot clock is a game mechanic that limits the time you can stay in a dungeon branch.
The clock is measured in decaAuts and it ticks down every time to do an action, e.g. move or attack. When the clock reaches 0, you die. The only way to replenish your Zot clock is to visit new levels.
Each branch has its own Zot clock. When you enter a new level, you get 6,000 decaAuts of time for the current branch, to the maximum of 27,000. The Abyss doesn't have a Zot clock, and you can explore it for unlimited time. Hell branches, including the Vestibule, share the same Zot clock. Also, the Zot clock stops for all branches when you pick up the Orb of Zot.
You can see the remaining time by pressing E. When the clock reaches 1,000, you get a warning and the Zot status effect, which shows how much time you have left.