Source code for this demo is available. Click Here to download.
You can also checkout the source code at GitHub
Market Place: https://marketplace.sitecore.net/Modules/S/Sitecron
For help with Cron Expressions you can use http://www.cronmaker.com/
You can get more information about the Cron triggers and examples from Quartz.NET Scheduler website at: http://www.quartz-scheduler.net/documentation/quartz-2.x/tutorial/crontriggers.html