Think that king might have a rather disrupted sleep schedule? It seems obviously insane to live like that, no? Instant reaction is "my god, why would you do that", right?
Consider that a totally ordinary middle class house in the West is arguably worse than that.
No wonder everyone "can't" sleep or "is just a night owl" (sure, some may actually be, not saying zero people are).
Frankly it's a miracle we get anydamnthing done, and sleep at all.
I'd encourage everyone to try candle-only lighting after sundown (or maybe extremely dim candle-temp electric lighting, though if you're just trying it briefly consider the candles, they're a bad idea for a bunch of reasons long-term but fine for a few days—you'd be surprised how little you need, I found two beeswax tapers were the minimum to read by without discomfort, but my eyes are still young-ish), no electric devices whatsoever (there's actually still a ton you can do—card games, board games, play music, read, draw, write, et c.), no whole-room lighting, just for a week or so. See if you're still a "night person" by day 7.
[EDIT] Bonus round on the thought experiment at the top: imagine the king is, despite this questionable decision, actually fairly responsible and leaves the castle to go run the kingdom during the day, most days, retiring to this ultra-carnival-home only late in the day. You'll expect that to go even worse as far as sleep is concerned, right?
I've spent considerable time in my travels in tropical nations. Two days there and I'm a completely different person.
The day starts at 5:30 AM, as soon as light arrives. And will you look at that, I'm jumping out of bed full of energy. Absolutely unimaginable back home. It's made possible because life slows down after 6PM. You eat, relax, and go to bed around 9pm. For the simple reason that there's nothing to do, and nobody else is doing anything either.
Unlimited light and distractions has made me a night owl, it's not a natural thing or character trait.
I admit my speculation that this explains at least 50% of modern sleep difficulty in developed countries is not based on hard data, but I'd say it's a pretty damn solid hypothesis. Yet everything's all "take magnesium" or "exercise more" or "use redshift" or whatever. Which is probably helpful, but seems like it's ignoring the elephant in the room, which is that we might have too much and too good always-available entertainment (and our lighting situation... after I got used to using candles, which was much faster than I expected, normal electric room lighting was shockingly bright, like I couldn't understand how I thought it was desirable or even OK before).
That said, it would be interesting if it became a fad (among the classes of means, naturally) to try to revert to premodern sleeping habits. Paleo-sleep, perhaps. It could lead to the return of biphasic sleep.
https://news.ycombinator.com/item?id=29886907
Or, perhaps, not:
https://www.theatlantic.com/science/archive/2015/10/the-many...
If anything, this is closer to a "Gods of the Copybook Headings" argument. "Too much of a good thing..." may be cliché and something only old fogeys say... but what if we're the ones making an error, in rolling our eyes at them? What if, not even that long ago, that was a bit silly applied to this particular thing (entertainment and nighttime lighting, chiefly) but no longer is?
I don't expect this problem to actually be fixed, but I do find all the casting about for "why do so many people have trouble sleeping, these days?" risible in light of what sure looks like the most obvious explanation, which never gets more than a personal-responsibility treatment ("put the phone in another room") which seems like a bad joke when you apply the medieval-king thought experiment. "Maybe the king should just not leave the bedroom, then?" LOL.
That means dark from before 17:00 to 8:00 and that is just too much. I can barely fit work into that.