I've found that about 30 minute interviews work about right for me. When I'm recording them, I may go as short as about 15 and as long as about 45. But 20-30 always feels like the sweet spot.
What I've noticed listening to a lot of lectures over the past few years are typically breaks at roughly: 90s, 5m, 10m, that 20--30m spot, 45--60m, 90m, and very occasionally a longer session, though I'd argue that 2h is about the maximum which can be sustained in a single session.
The shortest are just teasers, often commercial broadcast. They're not informative but more advisory, and really only advertisements for some additional content, which is the medium's strength.[1]
A 4--10m segment is a brief introduction to a topic, beginning with about the span of a noncommercial broadcast, and including the typical length of a quick YouTube video. You can actually cover quite a bit of the basics of a topic, or mesh together a number of topics into once related thread.
At 20m you're hitting one of the natural spans of human focus and the point at which attention starts to wander without some form of internal break or diversion. Longer presentations are often a fusion of 2--3 15--20 minute segments. I note that many well-structured podcasts aim for about this mark ("History of Philosophy" by Peter Adamson comes to mind.) If you're aiming to fill a 30 minute timeslot, 20--25m allows a bit of additional padding on either side for other filler as well.
Lecture presentations tend to run variously about 20, 30, 45, 50, or a full 60 minutes. Typically there's a Q&A session, and in an academic context, an introduction which I've timed many times at very nearly precisely 6 minutes. The meat of the lecture tends to run about 40-50 minutes, and again, that's a reasonably good intermediate introduction to many topics.[2] And of course, this falls squarely into standard one-hour scheduling blocks utilised by broadcasters and in scheduled event venues.
Most longer lectures I encounter tend to still limit the actual principle presentation to ~50-60m, with a longer Q&A. London School of Economics lecture series comes to mind.
Longer single-session lectures are almost always poorly-tailored and should have been split, edited, or both. I've found a few exceptions. Thorstein Chlupp can in fact talk quite informatively about net-zero residential design and construction in Alaska for upwards of two hours,[3] and Joseph Tainter's "Collapse" talk runs ... about 70 minutes, not terribly long, but over the 1h mark, without feeling thin.[4]
A well-prepared author seems generally to have a 1, 4, 10, 20, and ~50 minute versions of their talk. As I've often stalked speakers over various presentations, I've noticed cut points, transitions, and additional material usage practices.
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Notes:
1. To a first approximation, broadcast media offer infinitely expandable audience but strictly limited depth, whilst print is precisely the opposite. This means that the comparative strengths of each are in providing widespread awareness vs. providing in-depth exploration. Digital somewhat straddles this distinction.
2. A poorly-prepared speaker or interviewer is almost always starting to pad and tap-dance heavily by this point.
>At 20m you're hitting one of the natural spans of human focus and the point at which attention starts to wander without some form of internal break or diversion. Longer presentations are often a fusion of 2--3 15--20 minute segments.
Yeah. Even if things are thematically linked or parts of a longer story, pretty much any well-produced NPR/"NPR-style" podcast is broken down into segments as you say.
While there are certainly in-depth sessions that benefit from being 60-90 minutes, for most of the talks I give, I'll almost always pick a 20-30 minute option (which many conferences have these days) over a 45-60 minute one. Which, especially with pre-taped sessions, is increasingly an option. (It does get more logistically complicated with an in-person session because of the logistics involved going from room to room.)
Lightning talks (5-10min) I generally care less for. As you suggest, they're more a teaser than actual talk.
- This Thing You Did Know of Has Changed in This Way. (Status report.)
- This Thing You Did Know of Can Do Soemthing. (Very quick demo.)
The venue --- a meeting or conference, in which an audience has been assembled, but in which time/space are also limited, operates on audience inertia. Similar in ways to lead-in / follow-on audiences for broadcast programming, opening / warm-up acts in live performance, or pre-feature advertisements at cinemas (remember cinemas?). It takes time for an audience gathered to dissipate, or for an anticipated audience to appear.
(Not really anything to do with the original topic, just me noodling on elements / attributes of various media forms and their characteristics.)
But if you do happen to know that there's a lighting session and that the talks obviously do or don't fall into these categories, you might calibrate your own level of interest in the session.
I agree with that, especially the first 2 categories and especially when there's a connecting thread such as status reports about a related set of open source projects.
>It takes time for an audience gathered to dissipate, or for an anticipated audience to appear.
Shorter talks work a lot better as main stage sessions or as breakouts when there are very clear tracks that aren't likely to have a lot of audience overlap. Much as I do tend to prefer 25 minute or so sessions, I also appreciate that there's a lot of wasted time/motion if a lot of people are switching rooms every 30 minutes.
It felt like the intro to a podcast series (except without the podcast series).