function getTimeInSeconds(text) {
    let p = 0, sum = 0;
    while (text.length > 0) {
        sum += Math.pow(60, p) * text.substring(text.length - 2);
        text = text.substring(0, text.length - 3);
        p++;
    }
    return sum;
}

function convertTime(seconds) {
    let hours = ~~(seconds/3600);
    seconds = seconds - (hours*3600);
    let minutes = ~~(seconds/60);
    seconds = seconds - (minutes*60);

    console.log(`${hours}:${minutes}:${seconds}`);
}

let sum = 0;
document.querySelectorAll("span.style-scope.ytd-thumbnail-overlay-time-status-renderer").forEach(el => {
    let text = el.innerText;
    sum += getTimeInSeconds(text);
});

convertTime(sum);