Untitled

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">
    <title>DND time Tracker</title>
  </head>
  <body>
    <h1 id='demo'> </h1>
    <script>
    var hour = parseInt(prompt("Enter a Value", "0"), 10);
    var minute = parseInt(prompt("Enter a Value", "0"), 10);
      var colun=":"
      var n1=1

      document.getElementById("demo").innerHTML=hour+colun+minute

      function myFunction() {
    document.getElementById("hour +1").innerHTML = hour+n1+colun+minute;

}

</script>
<h1 id='demo'> </h1>

    <button onclick="myFunction()">Hour +1</button>
    <p id="hour +1"></p>

  </body>
</html>