Newish Casio user here. From what I understand, it's so that you can switch it to 24h after accidentally switching it to 12h and vice versa.
Been using Casio watches since 1983. That is exactly what it is for.
Plus, you don't have to manually convert from 24h to 12h time.
You are joking, but perhaps it's exactly what it's for.
Well done!
HN makes me laugh like twice a year – you're either the first or second!