Epoch or iso8601 date format?

Question

For passing times in JSON to/from a web API, why would I choose to use an ISO8601 string instead of simply the UTC epoch value? For example, both of these are the same:

Answer 1

Unix/Epoch Time
+ Compact

+ Easy to do arithmetic actions without any libraries, i.e. var tomorrow=now()+60*60*24

- Not human-readable

- Cannot represent dates before 1 January 1970

- Cannot represent dates after 19 January 2038 (if using Int32)

- Timezone and offset are "external" info, there is ambiguity if the value is UTC or any other offset.

- Officially the spec supports only seconds.

- When someone changes the value to milliseconds for better resolution, there is an ambiguity if the value is seconds or milliseconds.

- Older then ISO 8601 format

- Represents seconds since 1970 (as opposed to instant in time)

- Precision of seconds

ISO 8601 Time
+ Human readable

+ Represents instant in time, as opposed to seconds since 1970

+ Newer then Unix time format

+ Specifies representation of date, time, date-time, duration and interval!

+ Supports an offset representation

+ Precision of nanoseconds

- Less compact

- For any arithmetic actions, reach library is required (like java.time.OffsetDatetime)