I work in finance, and at a previous employer (not Robinhood), I partially rolled a datetime implementation. Mostly it was a wrapper around Boost Date Time [0].

I work in finance, and at a previous employer (not Robinhood), I partially rolled a datetime implementation. Mostly it was a wrapper around Boost Date Time [0]. It was a facade that smoothed out the interface and implemented some missing functionally, like a cross-platform strptime and loading of the Olson timezone database. I spent a better part of a year working on it (along with other things). Modeled the interface after Python's datetime module (which I think is one of the simpler and easy to use date-time libraries across various languages I've used). More than $20B USD trades using that library. The motivation was the firm used to use RogueWave's date-time facilities, but we moved away after they jacked up the licensing. Think we used to have a site-wide license, but they were moving to a per-core licensing, wanting something like $2K per core annually. Needless to say, testing was extensive. Overflows were found in Boost in far distant dates, had to work around those. Tested against a ton of historical dates. Tested against Northern and Southern Hemisphere daylight saving time (a lot of people don't realize that Southern is inverted from Northern). Learned a lot about timezones and the history of timezones along the way. [0] https://www.boost.org/doc/libs/1_72_0/doc/html/date_time.html https://www.boost.org/doc/libs/1_72_0/doc/html/date_time.htm...