This graph shows what share of your daily traffic is received at each hour of the day. Each bar represents one hour, and the bar's height represents the percentage of the daily traffic received for that hour. The number at the bottom of each bar is the percentage of visitor sessions received for that hour since the graph was created. You can use this information to find out, for instance, what your slowest time is during the day and arrange to do site maintenance at that time.
If the local time indicated above the graph is wrong you need to adjust your time zone in the Web-Stat Control Panel.