I'm trying to find statistics, research, etc, regarding the recommended length of elearning sessions. I have some info, but the more I have, the better.
I am getting a request to do some new technical training via online sessions 8 hrs a day. Since we estimate 40 hrs of material, this would be 1 full week, 8 hrs a day online. Yes, I hate this idea. I have our own internal statistics, but I am thinking that recommendations from outside the company would be awesome in helping to convince the requesting people that this is not the best way to do it.....some external numbers and recommendations would really help to back up my recommendations.

So if you are aware of where I can find resources, I would appreciate hearing from you. I am continuing to look myself also....

This is an interesting question and it got me thinking. First, let me say that by "session" I am assuming you mean a single activity: didactic learning, quiz, whatever.

I have always heard about limits of adult attention spans and that twenty minutes was the ideal maximum length for an eLearning session.

Then for smoe reason I thought about movies (motion pictures). I understand that the industry feels that 120 minutes is the ideal length. That is clearly longer than the eLearning sessions, but we like going to long movies far more than long eLearning.

Maybe it is the plush seats, dark room or big screen. I think, however, that it is the content and the presentation.

My new advice for length of eLearning sessions is "as long as you can keep the student fully engaged." In contrast to the movie theater offices have phones, bosses, email, coworkers, tweets and SMS messages, to name a few. These distractions tend to limit the ability of the student to be engaged. (Although, I have seen friends watch long movies at work...)

I think it is all about attention/engagement. If attention spans are getting shorter as some have said, then maybe the twenty minutes I mentioned above is too long. If you can do great content and prevent distractions, maybe twenty minutes may be too short.

A speaker at an event I recently attended said that web videos (think youtube) should not exceed 5 - 7 minutes. That is pretty short, but looking at youtube it may be a good length. I have also watched hour-long interviews on the web, when the speaker was engaging and I was interested in the topic. Internet marketers have done a lot of research in this area and so you might look at some of their sites.

Also check out The Entertainment Econcomy by Michael J Wolf.

I could go on and on, but I think that focusing on attention and engagement is the key. Given the factors I've mentioned above, I doubt you will find a good concrete numgber. (Consider a study with terrible content: how long can someone watch that???)

Here are some thoughts to reinforce travelerjjm's comments:

For classroom sessions, I expect my designers and trainers to change the nature of the activity every 20 minutes. This certainly doesn't mean the class takes a break every twenty minutes. . . . just no more than 20 minutes of the same type of activity in the room (presentation, demonstration, practice, etc.) Clearly the duration of experiential learning activities can be longer, so long as the learner is actively engaged.

It's been many years (dare I say decades) since I actually read the research this is based on, but I believe it was something like: most adults retain more of the first 15 minutes of content, and the last 5 minutes of content - this leads to an ideal duration of 20 minutes.

Something else to ponder: Does it have to be delivered all at once? What about 1/2 days (or shorter) completing elearning, mixed in with "real life" practice/scenarios/discussion. True blended learning, where there is a facilitated discussion of what was covered in the elearning. . .

Doug gives some excellent advice.

We are living in an A.D.D. world. You should set up training sessions accordingly..

You can make a session length either 10 minutes or 8 hrs...that really depends on how engaged you keep the learner...if the session is something that the learner just sits back and has to watch I would recommend not more than 10 minutes for one session. Of course you can put up multiple sessions and the learner decides when s/he wants to take up the sessions.

Considering that you are looking at building a "technical" training(and I assume it would have interesting interactivities to keep the learner engaged) I think it should not exceed 2~2.5 hrs. Anything more than that could be just falling on a clogged up brain...