I just found in the documentation that there is a boundary event that looks like a regular message that and I have to add manually
<boundaryEvent id="_4" name="TimerEvent" attachedToRef="_2" cancelActivity="false" >
<timerEventDefinition>
<timeCycle xs:type="tFormalExpression">500ms</timeCycle>
</timerEventDefinition>
</boundaryEvent>
FYI