This is a no-brainer.

But how short? Two minutes? Five minutes? Ten minutes? What does the evidence say? In Guo et. al. (2014) the authors found that learners begin to disengage from instructional videos after about eight minutes.

eLearning lessons

eLearning lessons are always chunked.

What's the difference between microlearning and chunking?

Chunked instruction relies on what precedes it and what follows it. There is a natural sequence. Microlessons stand alone, without requiring a fixed sequence with other microlessons.

So, microlessons should be under eight minutes.

What dictates the actual length of each microlesson?

Answer: The learning objective. Each microlesson should focus on a single learning objective.

Create short microlessons less than eight minutes focused on individual learning objectives.

How does adaptive questioning work?

There are many different algorithms for adaptive questioning but the basic idea in all of them is the same: Require the learner to answer questions until he/she has retired all the questions by answering them all correctly a fixed number of times in a row. We recommend two.

What are the best types of questions for retrieval practice?

Open response questions are best, but of course that takes a human grader, so most instructors use multiple choice questions. With some practice you can write higher cognitive level M/C questions that go beyond mere recognition. Standardized test developers do it all the time.

Do I need to create new content?

Probably not. You should have plenty of course material (videos, audios, PDFs, animated graphics, etc.) that can be repurposed into microlearning.

Remember to space the learning and adaptive questioning over time

Any other tips?

Take advantage of the spacing effect. (There is a lot of research that shows that spacing learning in small chunks over time [days or even weeks] is preferable to traditional massed learning.)