JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<div class="reglament"></div>

JavaScript

let dateStart = "2020-04-03";
      let timeStart = "11:00:02";
      
      var date = Date.parse(dateStart+' '+timeStart);
      
      var timeoutMin = 20;
      var timeout = timeoutMin * 60; 
      
      
      (function(){
      	let dateNow = new Date();
      	var t = (dateNow - date)/1000;
        if(t >= timeout){
					$(".reglament").text("Время вышло")
        }else{
          var showTime = timeout - t;
          var h = "0"+Math.floor(showTime/3600);
          var m = "0"+Math.floor(showTime%3600/60); 
          var s = "0"+ Math.floor(showTime%60);
          h = h.substr(-2);
          m = m.substr(-2);
          s = s.substr(-2);
          $(".reglament").text(`${h}:${m}:${s}`)
        }
      	setTimeout(arguments.callee,1000);
      })();