I have no data personally on this YET, but there's a new chapters feature being introduced to YouTube which I think may help my channel long term. I have a large drop off in my video starts, and I figure it's people people don't want to see any introduction, or they don't want to see my face. They want to get straight to the content. If I see a video where the introduction is too long, I'll simply leave. My past videos have annoying introductions which I wish I could edit out, but unfortunatly the start of the videos might not make sense, so I'm thinking about putting timestamps to the relevant parts that people want to see. I think this could potentially BOOST my watch time as people skip through my videos to find the parts that are relevant, rather than wasting their time making them HOPE I cover parts.
With anything, the only way to know is to try and experiment. which is why I plan on doing this, and It will be interesting to see how the data reflects.
I sense for how to instructionals, this will be invaluble.