IdleClock is a simple utility that logs the time when you go idle.
Edit IdleClock.properties to set how big an idle time you want to log. Editing the properties will need a restart of IdleClock to take effect.

Start using start.bat

If you double click the IdleClock.jar (assuming Java was correctly set up) or if you run start_silently[...].vbs, it will start without a console.
To stop it again after it, you have to kill Java in the Task Manager, so beware of doing that unless you know what you're doing.

TO SET UP AUTOSTART:
--WINDOWS--
First try to run the start.bat
If it tells you it can't find java, this method will not work.

But if start.bat runs without problems, simply right click on the start button, click on "Run.." and enter shell:startup
Alternatively, enter shell:startup in explorers location bar.
This should open the autostart directory, where you can simply put a link to start.bat (a link, do not copy or move the file or it won't work)
If you don't want a command window to pop up, instead of start.bat, use start_silently.vbs. Note tha to stop it again this way, you need to kill the java process.

--LINUX--
Open a terminal and enter
crontab -e
If it asks you which editor to use and you don't have experience with VIM etc, just use nano.
If it just opens VIM or something else, google a tutorial, VIM is a pain if you never used it
Simply add a line like
@reboot /path/to/java -jar "/path/to/IdleClock.jar"
(this is untested, I don't run linux any more)