What is the average time of an elearning course to be finish by a learner?

It's possible to get a fairly accurate estimate of "seat time" (how long it takes to complete a course) IF a course is fully narrated. In those cases, just determine how long it takes to play the audio/video files.

It's much tricker with other courses. Basically, seat time depends on how fast the learner reads. And even if you knew a person's average reading speed, it could still vary based on how familiar they already are with the content, how motivated they are to learn, etc.

But, yeah, people still want an estimated seat time. Here's how I come up with a range:

• I get a rough count of the number of words in the course. I do that by exporting the text into Microsoft Word (File > Translation > Export to Word), deleting the programming-related parts, and then seeing what Word shows as the word count.
• I divide the number of words by 120 (a low conversational speaking rate) to get a high estimate for the seat time.
• I divide the number of words by 200 (an average reading rate with 60% comprehension) to get a low estimate for the seat time.

ESTIMATE is the key word here. There will likely be some users who get through the course quicker, and some who take longer. But this provides a reasonable range -- with a lot less effort than setting up a focus group and timing how long users take to go through the course.