What is a Cron Expression in salesforce? How it can help us in salesforce?

Hi Mohit,

Apex classes to run at specific times, first implement the Schedulable interface for the class, then specify the schedule using either the Schedule Apex page in the Salesforce user interface, or the System.schedule method.

Ex: CRON Expression to run half past the hour
You can do it via code. The following code will schedule if for half an hour.

ProcessAccs pa= new ProcessAccs();
String cronStr = '0 30 * * * ?';
System.schedule('Process Job', cronStr, pa);

Thanks