Yep.
Actually, I’d put dealing with /understanding time-zones up there as one of the most complicated/confusing things in all of web development - so much so that many people don’t even realise the complexity until after they notice that the app they’ve built doesn’t work correctly for anyone outside their own timezone, due to the way they’ve dealt with time zones within the app. (or, when the clocks change for DST and suddenly everything breaks).
I’ve seen this a lot on apps like event management, hotel bookings, and project/task management applications, where bookings/weeks/time-slots etc. have to be consistent for all users, across different timezones, and if they aren’t then it throws off the entire thing (hotel rooms being available when they aren’t, weeks being shown with the wrong start-dates, project deadlines having the wrong dates for different users etc.).
So yeah… understanding time zones is definitely not easy.