It is not so easy.
25 hours cycle has been found on humans who work at arctic nights and havent enough light.
Our 24 hours cycle is driven by sunlight and hence by hormonal effects of melatonin. Production of melatonin is inhibited by strong light. Melatonin helps us to sleep so the 24h cycle is ready.
Slashdot Mirror
It is not so easy. 25 hours cycle has been found on humans who work at arctic nights and havent enough light. Our 24 hours cycle is driven by sunlight and hence by hormonal effects of melatonin. Production of melatonin is inhibited by strong light. Melatonin helps us to sleep so the 24h cycle is ready.