We do similar training, with continuing education that is similar to university courses and our approach is roughly one scorm package per week, with the scorm package containing anywhere between 30 minutes to 2 hours of content (which is also very dependent on the existing knowledge of the learner). This typically means between 10-30 'screens' of content.

We're translating that to Adapt and so far our approach is to still group things in a similar way, ie: aiming for 30 minutes to 60 minutes spent in each SCORM package, however it is organized. 

I think it might be best to think about what's the normal 'sit down learning session time' for your learner group? Do they only have 5-10 minutes to take a learning break before they have to do something else, or do they have the time and is the topic complex enough that it should be learned in bigger chunks of half an hour to an hour or more?