Yes, from 5.3 boundary events are supported on tasks. Looking at your process it seems like there is not timer definition given:
<boundaryEvent id="boundaryEvent_1" name="Boundary event" attachedToRef="userTask_1">
<outgoing>sequenceFlow_4</outgoing>
<timerEventDefinition id="timerEventDefinition_1"/>
</boundaryEvent>
and it should look like this:
<boundaryEvent id="_4" name="TimerEvent" attachedToRef="_2" >
<timerEventDefinition>
<timeCycle xsi:type="tFormalExpression">500ms</timeCycle>
</timerEventDefinition>
</boundaryEvent>
once you'll fix the process definition you'll be able to execute boundary events on a task.
HTH