The Short Answer
Seven minutes or less (before resetting the attention "timer")
The Longer Answer
The question to ask yourself is. How long will I "talk at" the learner before having the learner stay in the conversation?
Think about it. How long would you go on and on lecturing your learner and monologuing like a movie villain?
- Even professors lecturing will stop and ask the audience a question.
- In any day to day conversation, you are going to be sensitive to the ebb and flow of the conversation.
Good microlearning lessons are conversational. To the learner, it feels like a dialogue
An entire microlearning experience doesn't have to be 7 minutes or less if you are balancing the experience with engagements that require the learner to be involved.
Keep videos short, and only convey 1 key message per video. Keeping videos to a 3-5 minute time frame is optimal. That way you can add a couple of engagements to help reinforce the information - and still keep the lesson to about 7 minutes.