One interesting thing I learned while I tried to handle local time and NTP on a Raspberry Pico is that the TZ environment variable (that's usually something like "Etc/UTC" pointing to a zoneinfo file) can contain a TZ config as well, like "CET-1CEST,M3.5.0/2,M10.5.0/3". [1]
[1] https://sourceware.org/glibc/manual/2.42/html_node/TZ-Variab...