YouTube Tab Timer от Caspar333

This extension calculates the total watch time of all currently open YouTube video tabs. It also tells you the exact finishing time if you were to watch them all in a row. The popup shows a slim, clear total time and lets you expand a list for detailed video durations. The calculation updates automatically when you open or close YouTube tabs.
Key Features:
-Calculates total watch time of all open YouTube tabs
-Displays expected finish time
-Expandable details for each video
-Automatic updates when tabs change
-Changeable Colors

If you always open each YouTube video in a new tab, this add-on is perfect for you.