Documentation for Confluence 2.5.4 - 2.5.8.
Documentation for [Confluence Cloud] and the latest Confluence Server is available too.

Modify the cronExpression property of the mailPollTrigger bean in schedulingSubsystemContext.xml file.

\etc\java\schedulingSubsystemContext.xml

For example, the expression below will fire at 12pm (noon) every day:

 <property name="cronExpression">
   <value>0 0 12 * * ?</value> 
 </property>

Cron expression

You may also like to view an information on how to create Cron expressions to provide the ability to specify complex time combination.

http://quartz.sourceforge.net/javadoc/org/quartz/CronTrigger.html