I want to know the answer to the following question:
How long did the suppression of time clues study last?
All the background I'm provided with is that "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.". Is that enough to answer the question?
Answer: yes