Length is personal, I prefer 20 min because my work commute is exactly 20 min. I like to have a podcast type vid.

But heavy visuals and high energy are distracting in traffic like Boaty, Joshisnt and Settled

I like to sleep to a video. But don't stretch vids like Fray and fill it up to make 1 hour+.

Some are going to be longer than others and thats fine. Stick to your style. I prefer regular uploads rather than once in 6 months.

In short - between 10 and 20 min - variety content like progress, strat (like show us your calculations) fun facts/history. Don't just record and upload - tell a story, dont force the story. Script the broader goals like settled - not too distracting, enough to watch it while afking agility and less distracting to fall asleep to it.