[Fnoord]

Americans use DD/MM/YYYY (regardless of delimiter being e.g. / or - or .). We Dutch use MM/DD/YYYY. The latter results in sorting correct on month if its annual data. Over multiple years it breaks. ISO 8601 has my preference, though in MS Office I need to set to Japanese cause my version lacks the setting.

9.00 PM is very clear to mean 21.00 in 24H format. What isn't clear is if 9.00 is 12H or 24H format. 9.00 AM or 9.00 PM is. However if you may reasonably assume the user uses 24H format, it is clear. It always takes up less space to use 24H format, though 12H format is always clear. Except for TZ (timezone), both all time suffers from that.

[EDIT]Oops I messed up, and that's why I dislike these and prefer ISO8601. Although one nice thing about DD/MM/YYYY is that its little endian (which is easy to remember for laymen as going from small to big). Keeping rest of comment as is.[/EDIT]

[bigzyg33k]

This is incorrect, Americans use MM/DD/YYYY, and from my understanding most of the rest of the world (I think the Netherlands too) use DD/MM/YYYY

[illuminati1911]

Lot of Asian countries use YYYY/MM/DD like China, Japan, South Korea etc.

[smoyer]

American software engineers use ISO8601 or RFC3339 ... I just wrote 20210108 in my journal this morning (referring to a podcast episode published yesterday).

I'll admit I might be annoying to others ... my wife is specifically irritated when I write a time in military format (but my son has no problem reading it from my phone).

[arrosenberg]

I do that too, but I often replace the month with the 3 letter abbreviation to make it easier for others.

E.g. 2021JAN08.

[ci5er]

While I believe that most (?) of Europe uses DD/MM/YYYY, I am pretty sure that most of South East Asia (dunno about India and Nepal) use YYYY/MM/DD.

[ValentineC]

> I am pretty sure that most of South East Asia (dunno about India and Nepal) use YYYY/MM/DD.

I think you might have meant East Asia. I know Japan primarily uses YYYY/MM/DD.

Singapore, Malaysia, Indonesia, Thailand, Vietnam, Cambodia, Laos, Myanmar, etc (South East Asia) conventionally use DD/MM/YYYY. Interestingly, the Philippines seems to use MM/DD/YYYY.

This looks useful: https://en.wikipedia.org/wiki/Date_format_by_country