ytwl.js

window.yt = {h: 0, m: 0, s: 0}
document.querySelectorAll('.ytd-playlist-video-list-renderer .ytd-thumbnail-overlay-time-status-renderer').forEach((n) => {
    const split = n.innerText.split(':').map((i) => parseInt(i));
    const s = split[split.length-1];
    const m = split[split.length-2];
    const h = split.length > 2 ? split[0] : 0;
    window.yt.h += h;
    window.yt.m += m;
    window.yt.s += s;

    if (window.yt.s > 59) {
        window.yt.m ++;
        window.yt.s -= 60;
    }

    if (window.yt.m > 59) {
        window.yt.h ++;
        window.yt.m -= 60;
    }
});
console.log(`Total duration: ${window.yt.h}hrs ${window.yt.m}min ${window.yt.s}sec`);