A timestamp (<x id="START_ITALIC_TEXT" ctype="x-i" equiv-text="<i>"/>00:05<x id="CLOSE_ITALIC_TEXT" ctype="x-i" equiv-text="</i>"/> for example) is automatically converted into a link to a part of the video.
Chapters can also be set in the video description. Check the format <x id="START_LINK" ctype="x-a" equiv-text="<a href="https://docs.joinpeertube.org/use/create-upload-video#chapters" target="_blank">"/>in the PeerTube documentation<x id="CLOSE_LINK" ctype="x-a" equiv-text="</a>"/>