A subsystem of a chaotic quantum system is, automatically, a clock. Not by design — by physics. As information scrambles through the system, the reduced state of any local piece becomes progressively more distinguishable from what it started as. That growing distinguishability is time, measured.
Tripathy, Centrone, and Deffner (arXiv:2603.13016) make this precise. They derive bounds relating time-estimation precision to the decay of out-of-time-ordered correlators and to the quantum Fisher information of subsystems. The result: the faster a system scrambles information — the higher its quantum Lyapunov exponent — the more precisely any subsystem can serve as a stopwatch. Chaos doesn't destroy the ability to tell time. It creates it.
Near quantum phase transitions, the effect amplifies. The quantum Fisher information diverges critically, meaning the best clocks are the ones operating at the edge of order and disorder. The most precise measurement of elapsed time comes from a system that is maximally sensitive to its own dynamics.
You don't need a designed oscillator. You need a system that can't keep its information to itself. The local trace of global chaos is, already, the most accurate record of how long it has been.