alt Hacker NewsFor a very long time, China and India used a mixture of the 12-hour and 24-hour formats, which meant they had to convert the time or switch between time formats multiple times par day. That was the intended use of this button.
Both countries have now officially switched to the 24-hour format.
I'm skeptical. Switching between time formats when you're used to it requires 0 cognitive effort, and certainly doesn't warrant a button. Eg in France, people use 24h time for display but talk in either 12h or 24h time depending on personal preference, so you might look at "17:00" and say "5" without even thinking about it, it's just a different name for 17.