a simple script to run in the browser console to get the total length of youtube playlist

gistfile1.txt

const elements = document.getElementsByClassName('style-scope ytd-thumbnail-overlay-time-status-renderer');

let totalDuration = 0;

for(let el of elements){
    if(el.localName === 'span') {
        const durationString = el.innerText;
        const durationArr = durationString.split(':');

        let hours;
        let mins;
        let secs;

        if(durationArr.length === 3){
            hours = +durationArr[0];
            mins = +durationArr[1];
            secs= +durationArr[2];
        }else if(durationArr.length === 2){
            hours = 0;
            mins = +durationArr[0];
            secs = +durationArr[1];
        }

        const duration = hours + (mins / 60) + (secs / 3600);
        totalDuration += duration;
    }
}

const totalHours = Math.floor(totalDuration);
const __totalMins__ = (totalDuration - totalHours) * 60;
const totalMins = Math.floor(__totalMins__);
const __totalSecs__ = (__totalMins__ - totalMins) * 60;
const totalSecs = Math.floor(__totalSecs__);

const totalDurationString = `${totalHours} hours, ${totalMins} minutes and ${totalSecs} seconds`

console.log(`duration of the whole playlist is ${totalDurationString}`);

nice work