A scheduled event should be managed by an asynchronous listener.
If you use a synchronous listener, it will execute in the thread of the Quartz process dealing with the scheduling of that event, and such threads are on purpose kept in very small numbers (to avoid consuming unneeded resources — there's actually just one thread in the default platform, see templates/common/config/quartz.properties). If you write such a synchronous listener for a scheduled event then it should execute very quickly, but if it needs to it can also do asynchronous Work by passing a subclass of AbstractWork to the WorkManager method schedule.
But directly writing an asynchronous listener (which is implemented using a subclass of AbstractWork itself) is simpler.
