A Crash Course in Calendars, Dates, Time, and Time Zones - Marc Gregoire - CppCon 2021

From a channel Lumen includes in full: CppCon is the C++ community's main conference; its channel is full-length technical talks by compiler writers, committee members and industry engineers on the language, performance, concurrency and tooling, often with Bjarne Stroustrup and Herb Sutter themselves.

A 31-minute video from CppCon's catalogue; the title names its topic.

Video by CppCon, played through YouTube's embedded player.