Changing Cache Configuration Settings

Check On Interval Span - This defines the Time Interval at which the Cache should be checked for Stale Objects.
Interval - This Defines how long an object should be kept in Cache. 
Policy - This defined how the Interval should be used. If specified to Since Add, the Object is kept in Memory for the Interval Time and if set to Last Accessed its a Sliding Expiration Cache.
It is recommended that Check On Interval Span should be lower than the Interval Time. Also, the above cache is set for 30 Seconds. (Not 30 mins)

Cache definitions can be used to selectively or completely cache aliases, databases, or files at selected intervals.  Cache configuration can be created, edited and managed in the System > Administration > Cache folder.

Example

Navigate to the System > Administration > Cache folder to view your current cache definitions. By default, definitions exist for caching the most basic elements of the system - including memory, sessions, ORM data, and database records.

To edit a cache definition, right-click on Default.DefaultTimeCache, select Edit.

Caching intervals, policies and configurations are defined in the Edit Time Cache Definition pop-up.

Changes made in the Edit Time Cache Definition pop-up will automatically become system policy. For example, setting Check On Interval Span to 5 minutes and clicking OK will automatically configure the system to check the cache every 5 minutes.