If a timer is canceled inside of the @timeout method the scheduler will log an ERROR if the timer duration is longer than the intervall and an overlapping execution should be fired.
This is due to internal validatons.

This will not happen if the timer is canceled by an external process, here the scheduler is removed.

The log message is like this:
ERROR [org.jboss.as.ejb3] (EJB default - 3) WFLYEJB0164: Exception running timer task for timer [id=0bd9870b-568b-42f5-9bda-e1525c3500aa timedObjectId=ejb30-timer.ejb30-timer.SimpleTimerBean auto-timer?:false persistent?:true timerService=org.jboss.as.ejb3.timerservice.TimerServiceImpl@53ba1a7f initialExpiration=Tue Feb 09 17:19:32 CET 2016 intervalDuration(in milli sec)=5000 nextExpiration=Tue Feb 09 17:19:37 CET 2016 timerState=CANCELED info=SimpleTimerInfo description=A timer started every 5 seconds] on EJB ejb30-timer.ejb30-timer.SimpleTimerBean: javax.ejb.NoSuchObjectLocalException: WFLYEJB0331: Timer was canceled
at org.jboss.as.ejb3.timerservice.TimerImpl.assertTimerState(TimerImpl.java:459)
at org.jboss.as.ejb3.timerservice.TimerImpl.isPersistent(TimerImpl.java:215)
at org.jboss.as.ejb3.timerservice.TimerServiceImpl.shouldRun(TimerServiceImpl.java:1117)
at org.jboss.as.ejb3.timerservice.TimerTask.run(TimerTask.java:124)
at org.jboss.as.ejb3.timerservice.TimerServiceImpl$Task$1.run(TimerServiceImpl.java:1221)
at org.wildfly.extension.requestcontroller.RequestController$QueuedTask$1.run(RequestController.java:497)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
at org.jboss.threads.JBossThread.run(JBossThread.java:320)