It's a cute remark, but why is 50 minutes the right cutoff? For a technical talk it seems long. For an entertaining keynote it seems short. Movies are 90+ minutes.
I find movies have become too long — especially in recent years.
I consider 3+ hours indulgent (we get ice cream and beer, once or twice, during what used to be the reel changes here), but two and half hours is about right.
Two hours would be my bare minimum for "feature length", and when I see one and half hour "films" I wonder "why was this not made-for-TV"?
I doubt I will ever watch Heat again, unless over a couple days, and unless my child wants to I won't watch the Lord of the Rings again (and especially not The Hobbit movies; that was largely a waste of time, though I will gladly read The Hobbit at least once more before I die).
Mad Max: Fury Road (Black & Chrome version) I watched for the third time recently, but over two days.
Engaging conversation, though? I recently had the luxury of time and privilege of talking for three hours straight with a well-read college student. Not being a high school teacher anymore I'm out of touch with young-adult perspectives, and I have so many follow-up questions now.
You can improve this if you make it more varied, adding interactions, changing media, multiple speakers taking turns, that sort of thing, but having a rule of thumb helps.
And it fits calendars nicely, fifty minutes per talk, ten minutes break between, one talk per hour.
Yes, I suspect that's the real reason.
Yeah, personally I read it less as 50 minutes being some biological limit of human attention and more as once you go over people start thinking about how much longer you're going to be, how long it'll take to get to their class, weighing missing the end of this talk vs the start of the next one vs skipping their bathroom break/sprinting. Plus the added the distraction of people who have reached their limit getting up and squeezing their way past to leave.