These graphs show you different traffic metrics in percentage per hour of the day for a typical day: Visits, Page Views, Time-on-Site, Bounce Rates, Visit Depths, Conversions, etc. For each report the data is cumulative since the beginning of tracking.
For each graph, click on above the graph and to the right to get information on what is being measured. The concepts are the same as in the traffic over time reports, except that the data is presented as a percentage per hour of the day