TimeComments is a chrome extension that works with comments on YouTube (only ones that have timestamps).
You can find it here in Chrome Web Store.

You start watching a video,
this chrome extension wakes up
and then what happens?
.

It checks all the possible sources for timestamps. When it finds one, it makes it available to you by presenting it above timeline (marker) and in the view besides the video (text only). Comments, mentioned here, mean public comments, that users are posting bellow a video.

But there is also a bookmarking functionality. You can create a bookmark (maybe it shoud be called annotation or note to self) that refers to a specific time point in the video. This "bookmark" is a private comment, and is visible only to you in the same place and the same way as the public ones. There is also a page where you can view your bookmarks, all in one place. Just click on the extension icon and menu appears with this page as the first item.

You start watching a video,
half hour or maybe even longer
and then what happens?

[Light digression]

Sometimes in my Instagram feed I get some wise words, or read it in some book (not really), an example   
""" It is not that we have a short time to live, but that we waste a lot of it.     Seneca """    
and what just happened is that I watched half hour of an hour long video and then saw comments bellow and someone posted a comment with timestamps pointing me to what I really only need ... .

For each video it could be said that there is one moment or one part that is of most importance to you.
The main problem here is how to get to that part when it is all you really need/want to see.

Comments with timestamps help you not only by saving you time but they also add value to your experience in many ways, like when someone spot something that others have missed, maybe even a mistake in a university lecture, ... ... it happens.

There are already a few things that help. Certainly, authors can help with "Chapters". There are also tools for spotting patterns ( Machine Learning ) but I would argue that there is certain point on this road ( "to the good stuff" ) beyond which only humans can help other humans.

TimeComments is a project for empowering, enabling people in helping other fellow humans in answering "Where's the good stuff?" and generally to make helping in this respect make more sense if possible.