[bmarkovic]

In JSON the de facto standard for datetime is (because of JavaScript) very much the Unix msec timestamp (which is always in UTC) so while it's not hardcoded in spec you basically need to be an idiot not to do it like that, and removes one huge headache of XML dates which is timezones.

[halostatue]

I don’t think that I’ve ever seen msec timestamps passed around because JSON numbers are floats, which means that there’s a limit to the precision available (which is to imply as well that currency amounts should be passed as decimal strings in JSON for safety as well).

Suggesting that msec timestamps resolves timezone issues is naïve at best, because anytime you are passing something that refers to a real time (that is, it is significant to humans) rather than an instant time (that is, it is something like an event log timestamp), you are dealing with time in a particular place, which has human impact — cultural, legal, linguistic.

Passing around timestamps as RFC3339 UTC strings with timezone names and offsets (much like one should be doing in databases) is what would be recommended for real (human) times.