Sorry, sleep returned a Promise and you didn't await it. You called foo() immediately.

What you want there is to stop saying "day" and instead say "24 hours." This way the code is correct and you don't need to deal with time weirdness.

No, because if I want something to happen everyday at 12 o'clock, I have to wait for one day, if I wait for 24 hours, I will be off by an hour for half of the year.

Only if you live in one of the brain dead countries that observe the dst anachronism.

ok, but they still observe it and you still have to deal with it in your code.

our personal convictions don't change that fact.

Why do you want something to happen everyday at 12 o'clock specifically? If this is truly what you want, sure.

Lunch break reminder popup?

You seem to assume that a day always has 24 hours. Common (but not only) non-24h day lengths are: - 23 hours - 25 hours - 24 hours 1 second - 23 hours 59 minutes 59 seconds

You could assume that a day isn't exactly 24 hours, but it's close-ish to 24 hours. Nope, not even close.

And that assumes that we can treat an hour as a precise measure of time (we can't). On some systems, even a second is not a precise measure of time (second smearing).

To make things worse, those are "simple" edge cases.

Time is hard. I'm not sure if I can make any statement about time that is true.

I am saying that you shouldn't use day as a unit of time. You should use second, minute, hour, etc, because these have a constant duration. sleep(86400) should reliably make your thread sleep for at least 24 hours.

It depends on the context and the system you’re working with. In some systems, an hour may last 3599, 3600 or 3601 seconds (due to the leap second), a minute may be 59,60 or 61 seconds. Even a second is not always a „true” second.

There’s no single time unit that works for all situations.