Timing Adjustable requires that when a page enforces a time limit, such as a session timeout or a timed quiz, users are able to turn it off, extend it, or get significantly more time before it expires, unless the limit is essential and cannot be changed, like a real-time auction.
This matters for people who read slowly, use a screen reader, or need extra time to operate a keyboard or switch device. A checkout that silently expires a cart after two minutes with no warning is a common failure of this criterion.