The maintainers of the timezone database (tzdata) have been cleaning up some things lately. Namely, removing all the alias names that are not of the common IANA «region»/«city» form, but refer to specific countries, from the core package. NZ’s two timezones, “NZ” and “NZ-CHAT” were among these special cases. Also the ones beginning “US/” for the various timezones in the USA. <https://tracker.debian.org/news/1451157/accepted-tzdata-2023c-8-source-into-unstable/> <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1040997> <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1056908> These latter names are still available if you install the “tzdata-legacy” package. So you need to have that installed if you want to continue setting “TZ=NZ”. Either that, or learn to start saying “TZ=Pacific/Auckland” instead.