When you are on YouTube playlist page and want to know how long will the list play. You can paste it in console and run to get time in hh:mm:ss.

youtube_list_time.js

const all = [];

document
  .querySelectorAll('ytd-playlist-video-renderer ytd-thumbnail-overlay-time-status-renderer')
  .forEach(a => all.push(a.textContent.trim()));

let videosLength = 0;
all.forEach(a => {
  const timeSplit = a.split(':');
  videosLength += timeSplit[0]*60 + timeSplit[1]*1;
})

console.log("Total list running time: " + new Date(videosLength * 1000).toISOString().substr(11, 8));