There are a couple causes as to why your bar graph may visually show more than 1 hour in a 1 hour period time frame.
1. You are sorting the data on a user basis, and the user was logged into more than 1 tracked machine.
If the user uses PC-A and PC-B both within a selected timeframe, both PCs are tracked and the data will visually be shown based on their usage of both.
2. The user left a page open and the PC does not go into sleep/standby/hibernate mode.
The tracking begins when the user opens the page. The tracking will not provide the active/idle/total usage time until the page closes. So if the page is left running for 1+ hour, the currentware totals will not add into the data until it is closed, navigated away from, or the client does it time based reset. When the page data is sent over it will show the time used on that page from the starting period on the graph.