Anti Spoiler is the best extension to hide the video lengths and progress bar of videos and shows on YouTube.

You can quickly access the function with a simple click on the icon. 

Hide the video lengths, progress bar, and times.

Anti Spoiler will hide the video lengths, progress bar and times for all your channels, and you can set it to a specific channel.

If you are a fan of online video games, you can choose to hide video lengths, progress bar, and times for your favorite games.

Set Anti Spoiler as the first thing that you see when you go to YouTube.

You can configure the time that the extension will appear. 

After Anti Spoiler has been installed, you can set it to appear as a setting in the browser.