Optional. If set to a positive number, a computer is retired once it has existed for this many minutes, even if it is still busy or has never gone idle -- whichever of "idle" or "lifespan" happens first wins. New work stops being assigned to it as soon as its lifespan is reached; any build already running is allowed to finish, and the computer is then terminated once it goes idle.

Leave at 0 to disable this and keep the original behaviour: retire purely based on the Idle Timeout above, with no maximum age.