JSFiddle - React, Tailwind, and code Playground

HTML

<div id="worked">25:00</div>
<button type="button" onclick="update();">Start</button>

JavaScript

var $worked = $("#worked");

    function update() {
        var myTime = $worked.html();
        var ss = myTime.split(":");
        var dt = new Date();
        dt.setHours(0);
        dt.setMinutes(ss[0]);
        dt.setSeconds(ss[1]);
        
        var dt2 = new Date(dt.valueOf() - 1000);
        var temp = dt2.toTimeString().split(" ");
        var ts = temp[0].split(":");
        
        $worked.html(ts[1]+":"+ts[2]);
        if (ts[1]==0 && ts[2]==0){
            return 0;
        }
        else{
            setTimeout(update, 1000);
        }
    }
    setTimeout(update, 1000);