JavaScript How do I set this timer to a specific date?

[MichaelJackson69]

I want to understand how this timer function works, please can someone help me?
My goal is to set this timer to end: 2021.11.24 12:00 (UTC)

<script>
                        (function() {
                          var start = new Date;
                          start.setHours(0, 23.5, 0); // 11pm
 
                          function pad(num) {
                          return ("0" + parseInt(num)).substr(-2);
                          }
 
                          function tick() {
                          var now = new Date;
                          if (now > start) { // too late, go to tomorrow
                            start.setDate(start.getDate() + 1);
                          }
                          var remain = ((start - now) / 1000);
                          var hh = pad((0) % 60);
                          var mm = pad((remain / 60) % 60);
                          var ss = pad(remain % 60);
                          document.getElementById('time_hours').innerHTML = hh;
                          document.getElementById('time_minutes').innerHTML = mm;
                          document.getElementById('time_seconds').innerHTML = ss;
                          setTimeout(tick, 1000);
                          }
 
                          document.addEventListener('DOMContentLoaded', tick);
                        })();
</script>