Salesforce Schedule Jobs Examples

Hourly
     ClassName m = new ClassName();
     String sch = '0 0 * * * ?';
     system.schedule(' Update xyz (hourly)', sch, m);

Every 4 hours

     ClassName m = new ClassName();
     String sch = '0 0 0,4,8,12,16,20 * * ?';
     system.schedule(' Update xyz (every 4 hours)', sch, m);


Nightly @10pm

     ClassName m = new ClassName();
     String sch = '0 0 22 * * ?';
     system.schedule('Update xyz (Nightly @10pm)', sch, m);




Additional References:

• http://www.salesforce.com/us/developer/docs/apexcode/Content/apex_scheduler.htm
• http://goo.gl/vH2cz - get stock prices