A Timer-Element in a process-definition is the shortcut for "create-timer" on node-enter and "cancel-timer" on node-leave. But in the current implementation "timer" is hard coded resolved to the CreateTimerAction of jbpm.

For "create-timer" you can change the implementation class by change the configuration in the action.types.xml.

So when using "timer" the action class should be resolved via the action.types.xml as well, otherwise it is unintuitive and you cannot change the timer implementation easily.

I will commit the corresponding fix if I doesn't hear complaints.