<html> <script> delay = 10; bustime = 1605290400; function update() { delay = parseInt(document.getElementById("Delay").value); } setInterval(function() { var time = new Date().getTime() / 1000 - delay - bustime; var minus = ""; if (time < 0) { time = -time minus = "-"; } var hours = Math.trunc(time / 3600).toString(); var mins = Math.trunc((time % 3600) / 60).toString(); var secs = Math.trunc(time % 60).toString(); if (mins.length < 2) {mins = "0" + mins;} if (secs.length < 2) {secs = "0" + secs;} var formatted = minus + hours + ":" + mins + ":" + secs; document.getElementById("Clock").value = formatted; }, 1000); </script> <body> <input type="text" id="Clock" disabled /> <br/> Delay: <input type="text" id="Delay" value="10"/> <input type="button" id="Update" onclick="update()" value="Update Delay"/> </body> </html>