10-30 mins is alright, as long as it if full of information. I would suggest fine editing and cutting the parts with "eeh", "yeah we gonna wait on this for a minute to load", etc.
Also, as you are not making a lifestyle blog, you probably shouldn't film just your face all the time. I really like videos with good presentations, as if you are studying a course somewhere. The presentation can be vary simple, but serves as a good support for your speech and helps with structuring.
Yeah I will make sure to edit the video so I am not wasting anyone's time. I will have my face in the corner of the video likely the whole time. I will have a presentation in which I will show as well ( will fit more of the screen )
Some videos however might not feature my face.