On Wed 15 November 2017 18:14:20 Joerg Reisenweber wrote:
> there are 24 timezones

I have to correct myself, there are even more:
https://en.wikipedia.org/wiki/Time_zone#List_of_UTC_offsets

Anyway any particular moment is unambiguously identified by

unique_date, time_of_day, Timezone_designator_of_referential_system

IOW UTC timestamps have *one* date like every other timestamp, and UTC -
unlike other localized timestamps - is identical everywhere on this globe.
If a second and third alternative timestamp for other non-global timezones is
intended, it needs to be given separately:

2017-11-15 20:30 UTC
2017-11-16 04:30 HKT (Hong Kong)
2017-11-16 02:00 IST (Mumbai)

each of the three above (excl the towns in brackets) forms a valid unambiguous
timestamp. Note how UTC is correct everywhere - thus has no town assigned to
it - and identical to the other two. Merging them into one isn't possible and
also pointless. That also implies that for every timestanp it's irrelevant
which date other unrelated timezones might show for the same moment.

cheers
jOERG