Only inasmuch as I have to count from 12 because I don’t have the built-in instinct for that time format.

Nah, all you need is a little time to get used to it. It's my default setting on most of my devices. Once you get used to it, it's much easier to tell am vs pm at a glance, which is helpful when looking at timestamps (I work in IT, timestamps are important.)

Written as 1530, mostly only Americans who have been in the military and their friends will know what you mean.

15:30 they'll know it's a time.

No, it's just a familiarity thing and not even rare. It's like switching between metric and imperial units, if you're used to seeing something in one format it can be jarring to switch it in your head at a moments notice. A lot of people in the US use 24 hr time if they have a job relating to documentation or if their working hours can cause confusion.

For example, I have a client that has to document received material and they are open from 04:00 - 22:00. They use the 24 hr format because it is common to receive material at both 04:00 and 16:00 and having to make an extra column to type am or pm on their logs is stupid and is just another opportunity to make a mistake.

It's really not a big deal to anyone, if you get a job that uses it then you switch your phone and within a week or two it's second nature. Every blue moon someone will notice that all your clocks are set to a 24 hr clock and someone might ask why or what you do to need it, but that's it.

I grew up with a Betamax tape player under the family TV. It had a 24 hour clock and it was the timepiece in the house that was in the right spot to tell us all that it was bedtime. As a result I have an intuitive feel for the 24 hour clock. But if you haven’t used it regularly, which most ordinary Americans don’t, then yeah you just have to stop and do the arithmetic before you can connect 21:00 to your sense of time.

what is that, like extra noon or something?

I think they see it as some kind of metric time, and therefore something to be avoided at all costs.

They think it’s military time. I don’t know why because it doesn’t even read the same. Military would be something like thousand five hundred and thirty hours, we (people with 24h clocks) read it like fifteen thirty or three thirty in the afternoon, or even three thirty and omit the morning/afternoon part because it’s assumed from context.

THAT'S 1530, PRIVATE!
NOW GIVE ME 20!

Yes, it angers and confuses them.

No, we just have to do a little kindergarten (age 5) math, the difference between 12 and 15 is 3.

The 3rd-grade math (age 8) of figuring what time it will be 9 hours and 47 minutes later is equally difficult whether using 24h or am/pm. And may be easier using angles on an analog clockface, especially for an old fart like me.

The real problem with time isn't 12h vs 24h. It's the increments 12/24/60/30/15/5 when the rest of our system is base 10.

Oh and Daylight Savings. Jet lag without getting to go anywhere. Fuck that shit.

Pilot here, over been in the habit of using 12 hour for local time and 24 hour for zulu time. "12:45pm, 1745z"

No, it's just associated with military time and those who don't have friends from across the pond don't necessarily know that other countries use that time format.

Just kidding we're all just stupid