The time of the last refresh is shown in the refresh item accessible from the application menu.
It is important to note that this update time only reflects the last time the app was updated from within the app. It doesn't update when the widget updates as a full update only runs when you have Refresh Automatically on and it updates, or if you update from the update item within the app.
This was done to save battery/data, but sometimes causes customers to think that the app isn't updating how it is supposed to. If Refresh Automatically is turned off in the Launch Behavior area of settings, you have to manually refresh currently to make sure you have the latest data, but the widget should update as normal.