Joe : I feel so much safer knowing that potential officers only have an attention span of 5 to 6 minutes
Ed: I think it depends on what is being taught and the individual. I watch videos on turning on youtube all of the time that can run up to 15 minutes long. (I've watched longer) I subscribe to both capneddie and haydenHD. I think both produce good videos and both can range in time according to the projects.
With pens If you're talking about cutting down if you're showing a technique I'd show that and then maybe speed up the rest of the process. I know personally for me it takes me quite awhile to cut down acrylic. I'd probably say at least 10-15 minutes and that's with a carbide. No one needs to sit and watch that entire process..
If it's instructions and the lathe is to loud then I would use vegas to lower the sound track of the lathe sound and then do voice over. In the end I think you just need to find your 'style' and go with it.