The refresh interval for the layer must be set in the webmap. Once this is done, Operations Dashboard honors the refresh setting and update the map and any elements as requested by the interval.
http://doc.arcgis.com/en/operations-dashboard/help/create-web-maps-for-dashboards.htm
http://doc.arcgis.com/en/arcgis-online/create-maps/set-refresh-interval.htm
解决办法
Click duplicate or refresh browser after saving dashboard.