Youtube has added chapters to videos, not sure if anyone has seen what they look like, but here is more info from YT
For each of your uploaded videos, you can add video chapters. Chapters break up your video into sections, each with an individual preview. These chapters can help viewers by giving more info and context by allowing them to rewatch different parts of the video.
Turn on video chapters
To opt into video chapters, make sure that the first timestamp you list starts with 00:00. Your video should have at least three timestamps listed in ascending order. The minimum length for video chapters is 10 seconds.
- Sign in to YouTube.
- Go to the video you want to edit.
- Select EDIT VIDEO under the video.
- In the “Description” box of the “Add details” page, add a list of timestamps and titles.