[bsoriano]

Hmm it looks like TMDB API doesn't return duration for episodes only for movies. 

It doesn't. That's the reason I switched back for my scraping needs from TMDB to TVDB.
I think Trakt is returning duration for episodes.
Since this helper add-on uses Trakt too, maybe you could get the duration from Trakt.
I have no idea if what I am suggesting could work though   

Yeah unfortunately Trakt doesn't provide runtime by default in the calendar API request call. So it has to use the ?extended=full param which takes longer to make the request.

I've decided to add it for the NextAired calendar -- I think the trade-off of a longer wait time is worthwhile for duration since it is a pretty key piece of information for NextAired. @bsoriano - Can you test latest? Should now get duration. 

@jurialmunkey , confirmed, now duration is there.  Please do not forget about a solution for shows with the same name from different years.  Thanks.

Regards,

Bart