ffs they know time, as in the clock is a human construct and actually makes no GD difference, because we can choose to get up and go to sleep despite the numbers on some device?
or we can stick with " the numbers on this device control our health" that seems better somehow to people?
It's not that simple. Completely without your control, your body is waking up and going to sleep in response to a lot of triggers (there are actually a dozen or so circadian rhythms that regulate biological cycles, but most only ever talk about the day/night cycle...which is really quite important).
Light is a massive trigger that will jumpstart your wakeup process well before you are conscious of waking up, or our arbitrary concept of time. You can keep animals and bugs in thoroughly climate-controlled rooms or incubators for generations, and maybe one flash of light in the middle of a night cycle can thoroughly wreck their daily hormone cycling for weeks which, if this is the sort of thing you are studying, makes for a very bad month on the job. ....because now you've got to reestablish that cycle.
Which is to say, yes, people can adjust and adapt to any sort of cycle (it's not like there aren't places on the planet where people have lived for thousands of years with the type of light cycle and work life under DST). But it takes time. What I can say is that, if we're trying to set up a breeding colony for our mice and we need to flip the light cycle on them, or even adjust it up or down by an hour or two, we give them about a month or two to get back to normal. ....granted, this isn't something that I actually study or ever have, it's more of a part of husbandry that we have to deal with when working with model organisms--but light cycle is powerful enough to throw a wrench into the simple day-to-day behavior of your animals.
The issue here is just the switch in time every year and especially with DST, it's nearly a 2 hour flip in the morning sunrise for the first couple of weeks. After several months, it's no big deal and the reason we haven't really had any long term studies on this is because we haven't had an actual long-enough window of time to stay on a single cycle