Format the label in the time scale tooltip

src/scales/scale.time.js

@@ -403,6 +403,27 @@ function ticksFromTimestamps(values, majorUnit) {
 	return ticks;
 }
 
+function determineLabelFormat(data, timeOpts) {
+	var i, momentDate, hasTime;
+	var ilen = data.length;
+
+	// find the label with the most parts (milliseconds, minutes, etc.)
+	// format all labels with the same level of detail as the most specific label
+	for (i = 0; i < ilen; i++) {
+		momentDate = momentify(data[i], timeOpts);
+		if (momentDate.millisecond() !== 0) {
+			return 'MMM D, YYYY h:mm:ss.SSS a';
+		}
+		if (momentDate.second() !== 0 || momentDate.minute() !== 0 || momentDate.hour() !== 0) {
+			hasTime = true;
+		}
+	}
+	if (hasTime) {
+		return 'MMM D, YYYY h:mm:ss a';
+	}
+	return 'MMM D, YYYY';
+}
+
 module.exports = function(Chart) {
 
 	var defaultConfig = {
@@ -621,6 +642,7 @@ module.exports = function(Chart) {
 			me._majorUnit = determineMajorUnit(me._unit);
 			me._table = buildLookupTable(me._timestamps.data, min, max, options.distribution);
 			me._offsets = computeOffsets(me._table, ticks, min, max, options);
+			me._labelFormat = determineLabelFormat(me._timestamps.data, timeOpts);
 
 			return ticksFromTimestamps(ticks, me._majorUnit);
 		},
@@ -636,10 +658,13 @@ module.exports = function(Chart) {
 				label = me.getRightValue(value);
 			}
 			if (timeOpts.tooltipFormat) {
-				label = momentify(label, timeOpts).format(timeOpts.tooltipFormat);
+				return momentify(label, timeOpts).format(timeOpts.tooltipFormat);
+			}
+			if (typeof label === 'string') {
+				return label;
 			}
 
-			return label;
+			return momentify(label, timeOpts).format(me._labelFormat);
 		},
 
 		/**