JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//momentjs.com/downloads/moment.min.js"></script>
<script src="//momentjs.com/downloads/moment-timezone-with-data-2010-2020.min.js"></script>
<div id="output"></div>

JavaScript

var output = document.getElementById("output");

var start = moment("2015-01-01T00:00:00Z"); // Current time UTC value from server
var delta = start - moment();

setInterval(function(){
    var now = moment().add(delta,'ms');
    var m = now.tz("America/New_York");
    var s = m.format("YYYY-MM-DD h:mm:ss A");
    output.innerHTML = s;
}, 1000);