I see that in Nuxeo 5.6 the SchedulerService has moved packages and undertaken some renaming. I disovered this after looking further into a question on Nuxeo Answers.

In order to use the Scheduler Service effectively it would be extremely helpful if the underlying SchedulerServiceImpl registerSchedule method could handle the case where a CRON expression (in the schedule object) is null. When the CRON expression is null then a SimpleTrigger could be created that could be run 1 .. n times.

Something like...

if(cronexpression==null)
  use SimpleTrigger
else
  use CronTrigger
}

This would nicely support one-time events created in code without having to use a CRON expression. Would be even nicer if there was a way to automatically remove the one-time scheduled service on firing to avoid having to manually unregister. Maybe there's an easier way?