If it's a how to, then I don't particularly want to hear about how someone's day went. But if it's a vlogger then I want to know more about the person, as long as it's edited well to keep it flowing.
As for duration, I guess 5-6 minutes is an average watch for me, but I will watch much longer videos (up to 15 minutes) if the subject matter is right, or it's filled with a mix of things.