This is as good as my answer can get until the question gets more specific:
(function blink() {
  $('.demo').fadeOut(Math.random()*500).fadeIn(Math.random()*400, blink); 
})();<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<span class="demo">I'm blinking!</span>4
solved How to add randomness to the blink effect? [closed]