Time zone conversion is not automatic for datetime elements in the task payload when a task form is created. You must add the <af:convertDateTime> tag to enable time zone conversion on a datetime element. See any standard task header time label for an example. The following example shows a sample header:

<af:outputText value="#{bindings.createdDate.inputValue}"
                        id="ot15">
         <f:convertDateTime type="#{pageFlowScope.dt}"
                              timeZone="#{pageFlowScope.tz}"
                              dateStyle="#{pageFlowScope.df}"
                              timeStyle="#{pageFlowScope.tf}"/>
         </af:outputText>