AsyncWorkItemHandler supports only direct job scheduling meaning the job will be executed as soon as there is a worker thread available. That in most of the cases is desired though jbpm executor (that is behind async work item handler) supports "delayed" job execution.
That can be useful in use cases where a given operation should wait until it gets executed. Thus allowing users to specify initial delay before the job is eligible for execution can significantly simplify the processing.
One of a use cases for it is to skip intermediate timer event before the job in case there is a time delay needed before the job should run