The second topic, the main one that circadian scientists talk about, is chronic risks, and I believe they are more important to our health. To follow this logic, you have to believe that people will continue doing whatever it is they do today (e.g., going to bed at midnight), and won't shift their schedule around right away to optimize sleep--i.e. they will not recognize that their body clock is set mainly by sunlight. The campaign to change school start times has been going for 25+ years already, so fast changes here are pretty rare.
When the clocks change, people wake up at a different circadian time, and if that time is too early, it is associated with worse health outcomes.
Some large-scale epidemiological tools have been used to figure these things out. One compares the difference between sleep patterns on "work" days and "free" days - like how much do you sleep in on a weekend? (Till Roenneberg's "social jetlag"). A second method uses "position in timezone" - comparing people living on the eastern or western edge of a timezone in various ways.
Roenneberg's work from the mid-2000s showed that night owls suffer a lot under "wake up before the sun" kinds of schedules (their "social jetlag" is bigger) - it makes them fatter, more irritable, get more diabetes, etc. They don't go to bed any earlier, but they're forced to wake up earlier.
Next, when you look at timezone position (this has been done for millions of people), people on the western edge of a timezone (where the sun comes up later but the clock is set at the same time) are quite a bit worse off for cancer rates and obesity - 10-20% more for some kinds of cancers, and a roughly 20% increase in chances of being obese.
I'm worried about these chronic health problems, so I've been writing and advocating for standard time: https://medium.com/@herf/why-standard-time-is-better-e586b50...