There is also a distinction to be made between "technical" and "political" dependencies. Technical dependencies usually track some spec or common consensus, and political dependencies are e.g. timedate-library. Political dependencies are almost like business logic, because they have to track changing political decision made all over the world (or be local to some country).

Timedates are hard, and units may require even harder historical/present "political" tracking as how they are defined, and I would never want to maintain this kind of dependency: https://github.com/ryantenney/gnu-units/blob/master/units.da...

And what comes to timedate problems, I try to keep it simple if the project allows: store and operate with UTC timestamps everywhere and only temporarily convert to to local time (DSTs applied, if such) when displaying it in user-facing UI. This functionality/understanding can be locked into own 20-line microlibrary-dependency, which forces its responsible person to understand country's timezone and when e.g. DST changes and where/how/who decides DST changes and what APIs is used to get UTC time (and of course, its dependencies, e.g. NTP, and its dependencies. e.g. unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, which result is then combined with the Pope Gregory XIII's Gregorian calendar, which is a type of solar calendar mixed with religious event for fixing the time, which which is then finally corrected by rewinding/forwarding "the clock" because its too bright or dark for the politicians).