Beneath the Evertorch cathedral, where the Time leyline of Izzus presses closest to the Material plane, the rock does not keep ordinary duration. The few Tarkhon clergy who know of it call it the Labyrinth.
The Labyrinth was never built. It is the shape the leyline takes underground: a corridor whose length is not the same on the walk back, a tallow lamp set down still burning and found cold, or unlit, or guttering an hour after it should already have gone out. Surveyors sent down do not agree with one another. Sometimes they do not agree with themselves.
The flame above is the part of the Labyrinth that reaches daylight. The Evertorch burns without variation for the same reason the corridors below refuse to be measured. At the leyline's mouth time does not advance evenly, and the fire is held in a moment that does not move on. This is the older answer to the question Tarkhon's theologians prefer not to ask. They will ask what fuels the flame. They avoid asking why it is exempt from the wear that any fuel would imply.
The Izzus thread surfaces elsewhere, and stranger. In Besnoumeru, the second city of Nektuna, the Oracle Merchants turn a reliable profit closing deals a breath ahead of every rival on the floor; in Kerwin, a halfling king has outlived every emperor who ever taxed him; and beneath the ruined Tolarian capital of Elderran, where a mage-kings' machine tore the seam open outright, time has run wrong across a whole region for centuries. Whether these are the same thread of Izzus or separate fissures of it is not settled, and the Labyrinth is the only place anyone has tried to walk it on purpose.