> 00:00:00 to 24:59:59

thats a damn long day. my day is only from 00:00:00 to 23:59:59. where do you live that you have 25 hour days? /s

Sometimes I miss the home planet too.

The biggest difficulty for people will be forming new habits. The military time convention is familiar but cumbersome. Saying "I'll see you at 17 hundred hours" is not as convenient as "I'll see you at 17 o'clock" or simply "I'll see you at 17". The latter two sound a bit weird (especially the last one), but they're perfectly natural in other languages so it's just a matter of figuring out how to overcome the initial unfamiliarity in a large part of the population. I for one think this would be a great thing to standardise on just like SI.

> with time going from 00:00:00 to 24:59:59 a day

I guess the 24-hour system leads to confusion, too..? ;-)

> anglo-american

Do Spanish-American (and others) use kilos, metres, Celsius and all the rest? I'd assumed not, since the Quebecers I know use American measurements for their body and cooking. But I'd like to be wrong.

(You could also have meant anglophone, but that's too broad. 23:05 is fully understood in Britain, and the normal way to write the time on timetables and so on.)

Wikipedia:

"As of 2017, seven countries formally do not use the metric system as their main standard of measurement: the United States, Myanmar, Liberia,[3] Palau, Marshall Islands, the Federated States of Micronesia, and Samoa.[4] However, both Myanmar and Liberia are reportedly essentially metric, even without official legislation."

https://en.wikipedia.org/wiki/Metrication

Formal use is different that widespread consistent use, excluding the other system.

My observation, at least where I live, is that both systems are used in practice. Especially at grocery stores, where the aim seems to be intentional confusion. For example you buy oranges listed for 2.34 a pound, but at the register you are charged 5.74 a kilo. Where you charged the correct rate? Maybe? Maybe not?

well in germany you still say "ein pfund" (one pound) or "halbes pfund" (half pound) if you buy sausages/meat. but you mean 500g and not the real value of one pound. it's just that this is used because we got used to it. we also have a wierd system for the clock where we say "viertel vor" (a quarter to) or "viertel nach" (a quarter past). which is pretty common to say the time in quarters instead of values.

That would be 25 hours in a day

but when should 23:59:59.9999999 switch to 00:00:00?

Easy, 00:00:00 is one second after 23:59:59. You can use 24:00:00 in some circumstances to refer to the midnigt at the end of a day but it would be redundant say on a clock face.