jBPM jPDL User Guide 3.2.3
Table 21.20
Description of attribute cancel-event says:
"this attribute is only to be used in timers of tasks. it specifies the event on which the timer should be cancelled. by default, this is the task-end event, but it can be set to e.g. task-assign or task-start. The cancel-event types can be combined by specifying them in a comma separated list in the attribute. "

It works fine in state-node timers too, where it seems to be the easiest way to build a wait state of fixed duration.
(see http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4179889#4179889)

Also missing a statement indicating: "You cannot (and should not) cancel the timer within itself. "