Test whether the average cycle of sleeping and waking differs significantly from 24 hours.

Evolutionary theories often emphasize that humans have adapted to their physical environment.  One such theory hypothesizes that people must spontaneously follow a 24-hour cycle of sleeping and waking-even if they are not exposed to the usual pattern of sunlight. To test this notion, eight paid volunteers were placed (individually) in a room in that  there was no light from the outside and no clocks or other indications of time. They could turn the lights on and off as they wished. After a month in the room, each individual tended to develop a steady cycle.  Their cycles at the end of the study were as follows: 25, 27, 25, 23, 24, 25, 26, and 25.

Using the 5 percent level of significance, what should we conclude about the theory that 24 hours is the natural cycle?  (That is, does the average cycle length under these conditions differ significantly from 24 hours?)