udemy.js

var times = $(".lecture__item").not('.completed').find('.lecture__item__link__time').map(function() { return $(this).text() });
var reduced_time = times.map(function() { return this.split(":").map(function(str) { return parseInt(str) }).reduce(function(a, b)  { return a * 60 + b}) });
var seconds = Array.from(reduced_time).reduce(function(a, b) { return a + b }, 0);

Number.prototype.toHHMMSS = function () {
    var sec_num = parseInt(this, 10); // don't forget the second param
    var hours   = Math.floor(sec_num / 3600);
    var minutes = Math.floor((sec_num - (hours * 3600)) / 60);
    var seconds = sec_num - (hours * 3600) - (minutes * 60);

    if (hours   < 10) {hours   = "0"+hours;}
    if (minutes < 10) {minutes = "0"+minutes;}
    if (seconds < 10) {seconds = "0"+seconds;}
    var time    = hours+':'+minutes+':'+seconds;
    return time;
}

var one_point_five_time = seconds / 1.5

alert("Normal Time: " + seconds.toHHMMSS() + "\n  1.5x Time: " + one_point_five_time.toHHMMSS());