Question: When in the cycle do wake-sleep cycles break off from the circadian period?
Sentence: Studies by Nathaniel Kleitman in 1938 and by Derk-Jan Dijk and Charles Czeisler in the 1990s put human subjects on enforced 28-hour sleep–wake cycles, in constant dim light and with other time cues suppressed, for over a month.
Answer in sentence: no