This plugin extends the standard Moodle logging and reports / statistic gathering, to provide some 'time spent on course' type data. This is in fact a much discussed and often requested feature for Moodle (although there are many discussions about just how useful these types of statics really are - and how the act of measuring time does not equate to measuring learning, or even activity).
The above noted, it can still be really interesting and useful to see this data, and that's what this plugin give you in a very clear way
It is vital to setup correctly if the data is to be usable - see note below regarding documentation.
You can try this plugin yourself for real on our public plugins site: http://plugins.moodlebites.com