It's always funny to me when people assume that sleep works the same for everyone or that it is as simple as scheduling something on a calendar. Neither are true.
I think most people can change their sleeping habits. If you actually practice good sleep hygene and make consistent habits around sleep and you still can't get to sleep at a reasonable time, then you are not the norm and may have a medical condition.
Well, I can say for myself that the younger me adapted faster to timezone changes than I do now. That adaptation is presumably driven by the diurnal rhythms of the destination, but given that a fair amount of modern life is conducted under artificial light (and artificial darkness, for those who sleep in), it seems plausible that sleep patterns could be modified to some extent, through adjustment to the already-artificial diurnal cycle.
If you're in your twenties, you've probably spent 8+ years building up a habit of sleeping late. It's expected that it would take you a reasonable amount of time to break that.
As an anecdote in the opposite way, I am a sort-of night owl (my peak hours are roughly 10:00pm to 1:30am). As a teenager I was a late night, late morning (4am to 2pm) sleeper. Around 17, I started training at 7am, meaning I had to be up at 5:45 every morning. When I eventually quit after about 4 years, it took me another 4 years to un-learn the habit and move back to being an evening person.
I don't mean to nitpick, but I don't think it takes very long to break a sleep habit. I travel quite a bit and so am not only changing my actual sleep hours significantly (i.e. going to bed at what used to be my 4pm or whatever) but also changing them based on local timezones (so this job requires me to go to bed 2am local time, vs another job where I can go to bed 10pm local time). Anyway point is I'm usually adjusted within a week.
And I certainly adjusted from my "classes start at 7am" in highschool schedule to my "classes start at 12pm" schedule in college near instantaneously.
Your personal anecdotes say nothing useful about the experiences of other people.
I get pretty wiped out for a week when the clocks go forward or back. I'm only marginally productive when the sun is up, but get a huge amount done from about 8pm to 2am.
But so what? That's me. I don't expect the rest of the world to be the same.
Sleep is clearly very individual. Standard school/office hours are a hugely inefficient waste of the potential of tens of millions of people.
It should be possible to design a more flexible system. But we still have ridiculous notions that early risers are somehow the model of virtue, and everyone else should aspire to the same hours.
I've always found the best way to deal with jet lag is just to stay up until it's a normal time to go to bed in one's current timezone. Depending on where you are going/arriving from this can be quite a long stretch, but it generally gets me set on the local timezone within about two days.
It helps that I'm not very good at sleeping on airplanes unless I've been awake for >30 hours
It also helps to pre-empt it a little. The last few times I've flown long-distance, I've tried to adjust my sleeping a day or two in advance of flying and had very little problems.
You are right to say that we should not jump to conclusions, but it is appropriate to ask to what extent the phenomenon is affected by culture - for one thing, that would raise the question of whether, and to what extent, students might modify their behavior in response, possibly nullifying the effect after a while.
The paper itself seems to consider the effect to be largely genetic in origin, which I assume is probably a well-supported conclusion from other studies.
People at different ages have a different circadian rhythm. For teens and people in their early twenties it's a later rhythm. You can modify it, but it works to varying degrees. There have been several studies that showed that high school for example should start later because of this. It's currently only ideal for teachers. Blaming this on a lack of sleep hygiene and discipline doesn't really address the problem.
I'm not looking to any reference but a search should be trivial.
It's hard to say, but what this definitely does not show is that "starting university classes at 11am or later would improve learning." Rather it shows that, on average students, who have classes at 8 or 9 are most alert and receptive to learning by 11.
Unless student habits have changed a lot since my time, many of them are stumbling out of bed at 7:45 to make that 8am class and haven't had anything to eat or drink yet. They consider themselves “evening people” rather than “morning people" because that's when the most interesting parts of their lives are happening.
