2020-12-13 Alan E. Davis wrote:
>
> I think R would not be too unwieldy as a hammer here.  My use case  is a
> humble one: just take a several clock times in HH:MM format (utc) and
> adjust to  another timezone by adding or subtracting the relevant number
> of hours.  The day of week is not important; i will have to deal with
> it.  I did imagine a conditional subtraction by adding of subtracting
> 24:00 as needed.

Likely your approach is suitable for you and you could ignore my
comments. I just live in a city having longitude that should be (and it
was) the border between time zones, so majority do not like any
decision. Since cancellation of DST 10 years ago, local time has been
shifted 2 times...

To get time offset for some timezone, it is necessary to specify
timestamp, so a date is required in addition to time. Namely day of week
is mostly irrelevant.

Time transitions are usually arranged at night when most of people are
not active. Astronomers is a different case, that is why their chance to
face a timezone bug is higher.

When operations with arbitrary time zones are not required and a process
could be run with TZ variable set to desired time zone, libc functions
should work correctly. I have not tried elisp functions
https://www.gnu.org/software/emacs/manual/html_node/elisp/Time-Zone-Rules.html

A bookmark for those who still hopes to avoid complications with
time-related operations

Falsehoods programmers believe about time
https://infiniteundo.com/post/25326999628/falsehoods-programmers-believe-about-time