Only one application is counted at a time. If two or more applications are open, only the one that is active (that has the keyboard focus) is accumulating usage time. When the focus is changed to another application, the new application will accumulate the usage time. When we say the program tracks idle time, we mean that if there are no mouse moves or keystrokes for two minutes, no applications accumulate usage time. Instead the time is included in the total idle time.