JSFiddle - React, Tailwind, and code Playground

HTML

<div id="log"></div>

JavaScript

function roundTimeToHours(date, interval) {
    var time = date.getTime();
    var roundNumerator = 3600000 * interval; // 3600000 milliseconds in an hour
    var newTime = (Math.round(time / roundNumerator) * roundNumerator);
    date.setTime(newTime);

    return date;
}

var div = document.getElementById('log');

Date.prototype.addHours= function(h){
    this.setHours(this.getHours()+h);
    return this;
}

var i,
    d,
    html = '';

for (i = 0; i < 1440; i++) {
    d = new Date(2013, 8, 11);
    d = new Date(d.getTime() + i * 60000);

    html += d + '<br/>' + roundTimeToHours(d, 3).addHours(1) + '<br/><br/>';
}

div.innerHTML = html;