There are a bunch of events who use holiday times for other things.
In German we refer the time from first christmas day to first day of the next year just as “between the years”. (Some other languages do that as well) It seems the English term for that is “twelve nights”. That refers to a lunar calendar (354 days) being a bit shorter than a solar calendar (365.2422 days), which means you need to add leap days after the last day of the year to synchronize it with a solar calendar and the seasons which correlate with it. The roman calendar actually started with march.
Though it wouldn’t be hard to give christmas and the time around it more sciency names. Christmas is based on the winter solstice, the Roman calendar had winter solstice on 25th december and they celebrated the birth of their sun god, where they had parties and exchanged gifts.
The SI base unit for temperature is Kelvin with 0 K being the coldest possible temperature. 273.15 K is the melting point of ice. But it’s a lot better suited for temperature differences. Celsius is only a derived unit.
And well, all units and measurement systems had a lot of changes over time because some things turned out to be impractical or inaccurate.
Initially Celsius had 100° as the freezing point of water, 0° as the boiling point of water. Fahrenheit had 0° as the coldest temperature he could produce and the (wrong) average human body temperature at 90°. Kelvin was initially defined via Celsius, that got reversed, they have the same scale. There is also Rankine, which starts at 0 like Kelvin, but uses the Fahrenheit scale.
And the US partially uses SI units anyways, all units are derived from them to use their superior base unit definitions. This system came into existence to have unit definitions that are better reproducible and change less over time. Since everything was redefined and all numbers changed anyways, they also tried to make use of the “new” decimal representation of numbers. And new unit names were nice to create some general units, in contrast to foot and pound, which were always different from place to place, at times even from city to city.
I don’t expect the US to ever switch. The US switched to international yard and pound instead of switching to a decimal system. After US, UK, Canada, Australia, New Zealand and South Africa agreed on that one, all countries who remained using these units had a uniform definition for them. Since then you don’t need to know any longer which yard or pound it was. Though not all units got standardized by that.
And some countries didn’t drop all old units and metricized some instead. Even SI kept the ton(ne). You can’t know what 1t exactly means without knowing the context, it can be 2240lb, 2000lb or 1000kg (~2204.6226lb).