Why takes a long time to connect to socket io nodejs?

Question

Node.js

Online:

var socket = io("http://ip:port/");

socket.on('connect', function(data){
  console.log('Connected to server!');
});

in nodejs:

io.sockets.on('connection', function (socket) {
       online++;	
  socket.on('disconnect', function(){
          online--;
  });
});

The problem is that when a person visits the site, the line "console.log('Connected to server!');" sometimes it works right away, and sometimes after 3-4 seconds, the same thing happens if you just go to the address " http://ip:port/ ", sometimes it's an empty page, and sometimes it loads a few seconds first ...
What could be the problem ? where does the delay come from? VDS on Ubuntu 14