use a single, shared timestamps array between all pings

lib/time.js

@@ -0,0 +1,23 @@
+class TimeTracker {
+  constructor () {
+    this._points = []
+  }
+
+  newTimestamp () {
+    const timestamp = new Date().getTime()
+
+    this._points.push(timestamp)
+
+    if (this._points.length > 72) {
+      this._points.shift()
+    }
+
+    return timestamp
+  }
+
+  getPoints () {
+    return this._points
+  }
+}
+
+module.exports = TimeTracker