When creating web courses the content should be chunked into the smallest coherent units that still make sense based on the content, rather than on the clock. When users are doing self-paced training, they will be easily distracted. Creating a "6 hour" or a "3 hour" or even a "1 hour" module means that the users will have to chain themselves to the content for that time period and avoid any interruption. I doubt that they will be able to do that. Instead, content should be structured as little "pills" of knowledge that can be swallowed quickly or slowly, as the end-user wishes to do. One good option is to have a summary page with links to various presentations of the same material, and a few test questions on that material. This would constitute one "pill" of information. The user can take this, step away, come back, and proceed to the next "pill".
A level up from this would be the "courselet". A courselet is a small piece of content (perhaps a chapter or small course) that can be taken in a 15-20 minute period (for the typical user). If the user needs just-in-time training, a 15-20 minute period is about the most that can be expected for an uninterrupted experience.
Any videos or sound files should be kept 2 minutes or shorter. Otherwise, because watching a video or listening to audio are such passive experiences, the learner will focus instead on their e-mail or on playing a computer game while the content is being served to them.