I only program non-seriously for work on occasions and I’ve rarely used copy/pasted code. Except maybe some of my own code because of using lazy logic trees to deal with variation in the data being processed. Doesn’t need to be pretty or efficient. Just needs to work well enough so I do a less manual work.
DST means you also have things like CST vs CET and given some places start DST earlier or later than others and some ignore it all together, we probably have at least 50 time zones.
Always fun trying to schedule international regular meetings when suddenly there’s a week when half the people’s times changed and the other half’s times haven’t yet, so you try to figure out which time would exclude the fewest essential people.