In every project I've ever worked on, there's been somebody who must have been like, "HurDur Storing timestamps in UTC is for losers. Nyeaahh!"
And if I ever find that person, I'm going to get one of those foam pool noodles, and whack him/her over the head with it until I've successfully vented all my frustrations.
The only time using UTC breaks down is when any sort of time change gets involved.
If I say I want a reminder at 9am six months from now and you store that as UTC, a day light savings change will mean I get my reminder an hour early or late depending on where in the world I am
Programming aside, where I live in Southern Europe we have a tradition according to which leap years bring bad luck. After 2020, I don't know what to expect... nuclear apocalypse maybe?
I'm not worried about my code, I'm (very slightly) worried about all the date libraries I used because I didn't want code that shit again for the billionth time.
Yeah, I'm generally using the common data/time libraries in most (if not all) languages and I'm pretty sure they've all been through more than 1 leap year at this point. I just never 100% trust the code I don't control - 99.9% maybe, but never 100.
I worked in broadcasting (programming broadcasting applications), everything is done with PTP (Precise Time Protocol) and TC (timecode) in video. We had to support leap second, it's not as easy, but in the end, insert black frames for 1s and that's it.