One consequence of becoming interested in the length of documents is that I have given some attention to the related field of reading speed and time.
Over the years I have worked with a number of academics who proceed a workshop with a lengthy introduction. Sometimes this can be very long indeed! It is often claimed that the average human has an attention span of about 40 minutes. My own experience suggests that despite this an introduction should be kept to under 15 to 20 minutes duration. Adding more content serves no purpose if it does not register.
According to a Wikipedia article reading speed varies with language and writing system. Interestingly many people read much quicker than they are able to listen to spoken text. For English, reading speed is somewhere between 200 and 300 words per minute, bearing in mind that many people who will be reading an article in English may not have English as their first language. This means that a concise webpage of under 2,000 words will take about six to ten minutes of a reader’s time. If you have written a page of 8,000 words you should ask yourself will it interest a reader enough for them to spend 30 to 40 minutes of their time reading it?
A fellow writer suggested the use of videos to me. Similar criteria apply, although just as a video is more complex than a written page so too are the factors affecting its acceptability. Personally I find myself reluctant to watch videos of more than ten minutes length unless it promises to cover something I am particularly interested in. If a friend sends me a music clip I find I will give it about 30 to 45 secs before I decide to continue or not. If the intro seems to be one that is particularly drawn out I may jump forward to see if the track improves. With non-musical videos I probably will give it a bit longer to develop, but a lot will depend on the presentation. If a webpage is badly presented and/or poorly structured you can sometimes fish through it for the better parts. With videos this is more difficult so poor structure or presentation will often discourage a viewer.