JSFiddle - React, Tailwind, and code Playground

HTML

<div id="starDateTime"></div>

JavaScript

function toStarDate (date) {
  return date / 86400000 - date.getTimezoneOffset() / 1440 + 2440587.5;
};

var date = new Date();
setInterval(function timeChange() {
    date = new Date();
    document.getElementById('starDateTime').innerHTML = toStarDate(date);
}, 1000);