rule xxx
timer( cron: 0/30 * * * * * )
when
then
end

Exception in thread "main" java.lang.ArrayStoreException
at java.lang.System.arraycopy(Native Method)
at java.util.ArrayList.toArray(ArrayList.java:306)
at org.drools.compiler.PackageBuilder.getErrors(PackageBuilder.java:1274)
at org.drools.builder.impl.KnowledgeBuilderImpl.getErrors(KnowledgeBuilderImpl.java:70)

It would be a Good Thing if timer( cron: ) were documented. It deviates from UNIX crontab in at least two aspects.