Just Download & Extract the Above Zip File provided, then edit the script.js file with a good text / code editor like Sublime Text ( Check Google ) & then save the changes & then view the index.html file on the internet browser. That's all.
This is a Browser Based, Cross Platform, Supporting all Operating Systems, Easy Application.
If needed, you can change the value of the Timer from 15 seconds to any other value, by Searching & Replacing all occurences of 15 in index.html & script.js...