If I call the listTimers operation using the jmx-console I see all Stateless session Beans and all Message Driven Beans now, but only 5 of this 64 are really TimeObjects:
Output is for example:
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-core.jar,name=MbiWaehrFacade]
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-planning.jar,name=MbiProbfSelect]
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-costing.jar,name=PreliminaryCosting]
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-common.jar,name=Version]
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-core.jar,name=Calendar]
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-inventory.jar,name=StockManagement]
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-sales.jar,name=SalesOrder]
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-sales.jar,name=SalesItem]
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-core.jar,name=MailService]
handle: [id=1190398872277,target=[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-core.jar,name=MailService],first=21-Sep-2007 20:23:00.000,periode=60000]
[id=1190398872277,target=[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-core.jar,name=MailService],remaining=47564,periode=60000,in_timeout]
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-core.jar,name=MbiFistaFacade]
[target=jboss.j2ee:service=EJB3,ear=mbi2e-lafr-sb2000-ipc.ear,jar=ejb-session-core.jar,name=MessageRetrieval]

MailService implements TimeObject, but all others do not.
My Stateful Session Beans don't appear in the list, but all Stateless and MDBs do.