JSFiddle - React, Tailwind, and code Playground

HTML

<form><input type="text" id="inputid"></form>
<script type="text/javascript">f()</script>

<input id="pauseButton" type="button" value="Pause" onclick="pause()" />
<input id="resumeButton" type="button" value="Resume" onclick="resume()" disabled="disabled" />

JavaScript

var d1 = new Date();
d1.setHours(1,0,0);

var t = 0;

function f(){
    var h= d1.getHours();
    var m= d1.getMinutes();
    var s=d1.getSeconds();
    m= (m<10)?"0"+m: m;
    s= (s<10)? "0"+s : s;
    
    var el= document.getElementById("inputid");
    el.value= h+":"+m+":"+s;
    d1.setSeconds(d1.getSeconds()-1);
    if( h==0 && m==0 && s==0 ) clearTimeout(t)
    t= setTimeout(f,1000);
}

function pause(){
    clearTimeout(t);
    document.getElementById("pauseButton").disabled = "disabled";
    document.getElementById("resumeButton").disabled = "";
}


function resume(){
    t= setTimeout(f,1000);
    document.getElementById("pauseButton").disabled = "";
    document.getElementById("resumeButton").disabled = "disabled";
}