The interval is setted via the "timeout" Attribute. you can also make the interval periodic setting the "singleRun" attribute to false.
Source
<p:growl id="growl" showDetail="true" showSummary="true">
<p:autoUpdate />
</p:growl>
<pe:timer
timeout="5"
singleRun="false"
listener="#{basicTimerController.onTimeout}"
style="color: red;"/>
@Named
@RequestScoped
public class BasicTimerController implements Serializable {
private static final long serialVersionUID = 1L;
public void onTimeout() {
FacesContext.getCurrentInstance().addMessage(null, new FacesMessage(FacesMessage.SEVERITY_ERROR, "BOOM", null));
}
}