I wrote another user script that can be installed using TamperMonkey for Chrome or GreaseMonkey for Firefox.
The purpose for this user script is to append to the metadata displayed in the 'Up next' pane on Youtube so that it includes the elapsed time since the video was uploaded. I did this because, while watching videos on Youtube, I'd see the videos coming up next and couldn't remember whether or not I'd seen them before. Now, with this script, I can more accurately guess if I've seen a video before based on how long ago it has been uploaded.
Install from GreasyFork:
https://greasyfork.org/en/scripts/38439-youtube-up-next-time-since-upload
Install manually from Github:
https://raw.githubusercontent.com/deelawn/user-scripts/master/youtubeupnextuploadtime.user.js
How the 'Up next' pane looks when the script is running:
Note:
Some of the times in the image above are incorrect. This is because I didn't have an sufficiently long interval set, causing incorrect elapsed time values to be retrieved. This is fixed.