But you’re both doing a conversion in this case also? You’re both mentally converting the UTC time into your local idea of what part of the day that is.
With time zones you don’t do that mental conversion because that part is the same, you do a different conversion for the offset.
There’s a conversion with either system.
Granted, it’s probably my favourite wallpaper app too and I only learned about it yesterday. It’s also my least favourite for the same reason. I’ve never used it, or any wallpaper app, or even knew they are a thing so it wins by default.