Well unfortunately it is a guessing game. I do my guessing by right clicking on the graph, select the source tab, and the set the start and end times to something easy to understand like 6am-6pm. if you add a vertical grid it should be not too difficult determine when the lunchtime rush is.
If you would like a graph with the time as a label, consider using LogParser (Microsoft) on a machine with excel installed (excel needed to use charting functions.)