Correct tooltip timestamp (#6283)

Corrects #6275, follows #6211

public/app/plugins/panel/graph/graph_tooltip.js

@@ -149,8 +149,6 @@ function ($, _) {
 
         seriesHtml = '';
 
-        absoluteTime = dashboard.formatDate(seriesHoverInfo.time, tooltipFormat);
-
         // Dynamically reorder the hovercard for the current time point if the
         // option is enabled, sort by yaxis by default.
         if (panel.tooltip.sort === 2) {
@@ -161,13 +159,14 @@ function ($, _) {
           seriesHoverInfo.sort(function(a, b) {
             return a.value - b.value;
           });
-        }
-        else {
+        } else {
           seriesHoverInfo.sort(function(a, b) {
             return a.yaxis - b.yaxis;
           });
         }
 
+        var distance, time;
+
         for (i = 0; i < seriesHoverInfo.length; i++) {
           hoverInfo = seriesHoverInfo[i];
 
@@ -175,6 +174,11 @@ function ($, _) {
             continue;
           }
 
+          if (! distance || hoverInfo.distance < distance) {
+            distance = hoverInfo.distance;
+            time = hoverInfo.time;
+          }
+
           var highlightClass = '';
           if (item && i === item.seriesIndex) {
             highlightClass = 'graph-tooltip-list-item--highlight';
@@ -190,6 +194,7 @@ function ($, _) {
           plot.highlight(hoverInfo.index, hoverInfo.hoverIndex);
         }
 
+        absoluteTime = dashboard.formatDate(time, tooltipFormat);
         self.showTooltip(absoluteTime, seriesHtml, pos);
       }
       // single series tooltip