Estimated Seat Time or Duration of Course

I have been at many eLearning agencies and estimating seat time is always a massive, complex hurdle. I would suggest using a calculation based on content and complexity over anything built in or averaged from users so that your estimates are consistent, demonstrable, and replicatable. 

I suggest using http://touchcalc.com/calculators/mergener

If you have video you would need to add that on top, images would need to be accounted for in the wordcount or complexity. A diagram could have no words for example, but add to the complexity of the content, or an infographic would have words that can be tracked into the estimate.

Using an average seat time from a group is not a great way to calculate seat time in my opinion. Often clients will also do this and will propose their own seat time in response, essentially trying to cut the cost and it's hard to account for how different learners will have different incentives to run through content fast or slow meaning your estimates will end up being meaningless.

I would also suggest avoiding the storyline seat time estimator. I believe it is using the timeline as it's main source of estimation, meaning you could put all of Tale of Two Cities on a slide in an interaction, set the timeline to 10 seconds, and the estimator will just tell you the seat time is 10 seconds.