I personally prefer the 24-hour clock to the more common 12-hour clock. On most OSes and even some obscure devices such as my wristwatch, it's possible to selectively output a 24-hour time. It turns out there was a way to do this with my clock radio too.
My clock is a Lloyd's J274 circa 1978. The clock portion is based on a Sanyo LM8361 chip, which has a select pin for a 24-hour mode. The clock physically has no switch to enable this, but it turns out that by soldering a wire from pin 38 to ground, it's easily enabled, making for a fairly quick hack. Unfortunately I later found out that Lloyd's skimped on their LED panel and only included a "1" in their ten-hours place, so times past 19:59 are displayed as 10:00 to 13:59. I'm looking into a workaround that involves three more LEDs to get a proper "2" character to be displayed.
I'm also aware that Antony will not approve of this.