In Stream classic you can type a time code in the description of the video which will be clickable.
If you upload videos to SharePoint which is our future path, we have a roadmap item slated for starting roll out in March that adds an entire feature for audio and video table of contents. You open the table of contents pane, scrub to a point in time for the video or audio and then add a chapter at that point with a specific name. Viewers then see the chapters on the timeline or can click from the table of contents side pane.
Https://aka.ms/streamroadmapdates