The body's natural clock is more than 24 hours a day anyways. 
More recent research has shown that adults have a built-in day, which averages about 24 hours; indoor lighting does affect circadian rhythms; and most people attain their best-quality sleep during their chronotype-determined sleep periods. A study by Czeisler et al. at Harvard found the range for normal, healthy adults of all ages to be quite narrow: 24 hours and 11 minutes ± 16 minutes. The "clock" resets itself daily to the 24-hour cycle of the Earth's rotation.
So it's between 24.18 and 24.62 hours when shielded from clock resetting factors (magnetic fields, lights, etc).