Distraction Notifier is a simple script, showing alert on page load and periodically at defined time intervals. It can be run on chosen websites using browser extensions, ie. Custom JavaScript for websites
Ultimately this script will be a browser extension.
Example usage:
var notifier = new DistractionNotifier();
notifier.init('STOP! This page is wasting your time.\n\n' +
'Button "OK" will close this page. Click "cancel", if you'd like to stay here.\n\n' +
'This message will show up again in 5 minutes.', 5 * 60);