Hi,
I just tried this with texlua 1.10.0:

--------------------------------------------
  local function time_of_day (TZ)
    os.setenv('TZ', TZ)
    local time = os.gettimeofday()
    print(os.date('%c', math.floor(time)))
  end

  time_of_day ('America/New_York')
  time_of_day ('Europe/Paris')
  time_of_day ('Asia/Tokyo')
--------------------------------------------

It seems that os.setenv() is only executed once and all results are
in Eastern Standard Time:

  Fri Feb 21 16:37:13 2020
  Fri Feb 21 16:37:13 2020
  Fri Feb 21 16:37:13 2020

When I call "time_of_day ('Asia/Tokyo')" first I get

  Sat Feb 22 06:39:46 2020
  Sat Feb 22 06:39:46 2020
  Sat Feb 22 06:39:46 2020

Is it possible to fix this behavior?