"Many of them even had cycles lasting up to forty-eight hours, which included thirty-six hours of being active followed by twelve to fourteen hours of sleep."
The Body Electric also mentions experiments where people developed sleep-wake cycles that were multiples of a typical cycle;
now commencing an experiment of a sleep-wake cycle lasting roughly 12-36 to 14-34 hrs with a lizard lamp and consistent syncing with the sunrises, sunsets, and Schumann resonance;
in 1972 a man went into an underground cave in order to study chronobiology, followed by others attempting similar conditions:
https://howandwhys.com/michel-siffre-time-experiment-body-sleep-cycle/
The Body Electric also mentions experiments where people developed sleep-wake cycles that were multiples of a typical cycle;
now commencing an experiment of a sleep-wake cycle lasting roughly 12-36 to 14-34 hrs with a lizard lamp and consistent syncing with the sunrises, sunsets, and Schumann resonance;