SOURCE

let date=new Date();
let h=5;//进制是5.
 var timer=setInterval(()=>{
 let sec= new Date().getSeconds()-date.getSeconds();
  if(sec%h==0)
  {
    if(sec/h==3)
        clearInterval(timer);
     document.getElementById('min').value=Math.ceil(sec/h);
  }
  document.getElementById('sec').value=sec%h;
},1000);

  分<input type="text" value='0' id='min'/><br />
  秒<input type="text" value='0' id='sec'/>