When in university, I wrote a paper about the dropping relevance of mass broadcast media (i.e. TV and radio) compared to on-demand media sources (i.e. iPlayer, MixCloud, etc) and offered potential methods to encourage watching live programming instead of watching on-demand (i.e. audience participation, gamification, etc).
But what about from a production point of view? How does developing a "TV [sic] series" intended for an on-demand service from the start vary to one intended for broadcast? Series such as "House of Cards" and the new season of "Black Mirror" are two such series. Billed as "Netflix Originals", they are created for and on-behalf of the on-demand service provider as original content designed to add additional reasoning to use their service compared to other such websites or even traditional disc-based media.
One such limitation of broadcast media is the scheduling around other programming, plus any advertising of course. Here's an example schedule for a generic "1 hour" TV programme broadcasting in the UK on a commercial channel:
11:02 Programme starts
11:14 Cut to advertisement break
11:17 Return to programme
11:29 Cut to advertisement break
11:32 Return to programme
11:44 Cut to advertisement break
11:47 Return to programme
11:58 Programme ends
12:02 Next programme
So the programme itself is actually 46 minutes long, but the adverts pad it out to a 60 minute "block". Because this amount of adverts and the timing of which is fairly standard in the UK, you can't make a 55 minute episode and expect it to be broadcast without special arrangement from the channel. Similarly, if your series is weekly, you can't make the lengths of episodes vary and expect the channel to mess with the schedule each time. You have to be consistent and roughly a standard episode length. For minor adjustments, the channel can put in some idents or trailers on top of the usual adverts to pad for time, but there's only so much they can do.
Staying on the theme of TV scheduling, you have to take into account the timings of advertisement breaks and add them into your programme yourself. You don't want the channel to cut to a break mid-sentence, do you? Scenes are often timed around the advertisement breaks if it's made for TV. They'll also be designed to keep people tuned in, as the ad breaks are when people are most likely to tune out. In other words, you want to end each part of an episode as a cliffhanger so people stay tuned in.
Also regarding time is the suitability of language and visuals for the time your programme will be broadcast. TV in the UK is well known for having a set time where content can begin to be unsuitable for children, and that's at 9pm, known as the "watershed". After this time, strong language, violence, etc is permitted, though this isn't a binary rule as the further away from the watershed it is (the later at night it is), the more appropriate said content is. You will have to make your programme taking into account the time of day it will be shown and, thus, the audience watching it. Radio doesn't have a set watershed, and instead relies on being particularly aware of the audience and whether those who would be offended are expected to be listening at the time broadcast. Side note: This makes broadcasting anything particularly strong on radio very dangerous and is why I am very keen on not having any swearing on my show, even though I could probably argue that kids won't be listening to it.
So where does this leave on-demand? Well, for the most part, premium on-demand services have no advertisements within the programmes, so there's no concern about timing scenes to finish at the right moments and taking into account the breaks, etc. This isn't true for all services, though. Were Channel 4, for example, to create programming exclusive to on-demand with no intent to broadcast them ever, the programmes will still have advertisement breaks within the episodes as that's how Channel 4 is funded. As such, there wouldn't be much change in production timing compared to broadcasting it. However, for all platforms, there's now no issue in the length of the episodes, as there's no further programming to fit in around. Episodes could vary from 50 minutes to 150 minutes for specials without needing to clear it with the channel scheduling first. This allows for a lot more creative freedom in creating programmes as there may be moments that would've been cut out to shrink the episode down to a single block, or scenes could've been dragged out to fill the full block.
What does make a difference however, regardless of on-demand platform, is the age gating of content compared to watersheds and audience estimation. On-demand services have parental controls and other settings to restrict or limit access to stronger material for those more sensitive to it. As such, knowing when your programme will be viewed isn't an issue any more, as the platform will do the protection work for you.
One last note is that, while programming may be made for on-demand in the first instance, it may still be considered for broadcasting in future as an additional revenue stream. In which case, it could regardless be formatted around hypothetical advert breaks in the event that this happened in the future. Same goes for the length of the episode. Until broadcast TV dies a death completely, I suspect this will be the way to go unless the on-demand company takes control of all rights of the series in question (Netflix Originals, for example, will almost certainly never be on another streaming service or on TV).
For a quick example of a series taking this extra freedom in its stride, take a look at Black Mirror. Originally made for Channel 4, the episodes were 44 minutes long save for the two longer specials ("Fifteen Million Merits" and "White Christmas"). At 44 minutes, that's similar to the example I made up above and covers for the advert breaks and idents/trailers. Season 3 is Netflix exclusive and so far the runtimes have been 63, 57, 52, 61, 60 and 89 minutes. A range of 11 minutes across the first five, then a movie length finale to the series. Considering each episode is self-contained, this series in paticular makes good use of the freedom to vary the length of each episode and not feel confined to television scheduling. Of course, you need a guideline length of time to aim for, which is why it's still around an hour, but it means you can adjust it to be perfect, rather than settling for what fits a TV slot.