How to Schedule a Batch Job every 30 Minutes

1. Create a class that implements the Batchable and Schedulable interfaces
2. Connect to the Developer Console
3. Go to Debug / Open Execute Anonymous Window
4. Enter this code and execute it
5. Monitor your scheduled jobs
6. If you need to run the job more often, like every 15 minutes, create two additional jobs:one for 15 minutes, and one for 45 minutes.

System.schedule('myJob_00', '0 0 * * * ?', new myClass());
System.schedule('myJob_30', '0 30 * * * ?', new myClass());

by Vladimir Martinov