issue #4747 - add date and time units to singlestat panel.

public/app/core/utils/kbn.js

 define([
   'jquery',
   'lodash',
+  'moment'
 ],
-function($, _) {
+function($, _, moment) {
   'use strict';
 
   var kbn = {};
@@ -580,6 +581,20 @@ function($, _) {
     }
   };
 
+  // Date and time
+  kbn.toDateTime = function(size, timeScale) {
+    var datetime = moment(size * timeScale);
+    return datetime.format('YYYY-MM-DD hh:mm:ss');
+  };
+
+  kbn.valueFormats.datems = function(size) {
+    return kbn.toDateTime(size, 1000);
+  };
+
+  kbn.valueFormats.dates = function(size) {
+    return kbn.toDateTime(size, 1);
+  };
+
   ///// FORMAT MENU /////
 
   kbn.getUnitFormats = function() {
@@ -619,6 +634,13 @@ function($, _) {
         ]
       },
       {
+        text: 'date and time',
+        submenu: [
+          {text: 'date (ms)', value: 'datems'},
+          {text: 'date (s)',  value: 'dates' }
+        ]
+      },
+      {
         text: 'data',
         submenu: [
           {text: 'bits',      value: 'bits'  },