code: private AjaxFormComponentUpdatingBehavior createAjax(final QueryParameter parameter, final IModel model, final Component component, final String time) {
          return new AjaxFormComponentUpdatingBehavior("onchange") {
  
              @SuppressWarnings("unchecked")
  			@Override
              protected void onUpdate(AjaxRequestTarget target) {
              	// @todo wicket 1.5 does not update model for DateField and DateTimeField
                  // https://issues.apache.org/jira/browse/WICKET-4496	
                  // use this as an workaround	
              	if ((model == null) || (model.getObject() == null)) {
              		return;
              	}
              	Date date = (Date)model.getObject();
              	if ("hours".equals(time)) {
              		date = DateUtil.setHours(date, (Integer)component.getDefaultModelObject());
              	} else if ("minutes".equals(time)) {
              		date = DateUtil.setMinutes(date, (Integer)component.getDefaultModelObject());
              	}            	
  				model.setObject(date);
  				
                  populateDependentParameters(parameter, target, false);
              }
  
          };
      }
docs: used to update hours and minutes