On my Kindle 3, changing the default English locale (en-US.utf8) to a 24h locale, e.g. German (de-DE.utf8), in debug mode followed by a restart did the trick.
Code:
;debugOn
~changeLocale de-DE.utf8
;debugOff
I don't know if this works on the DXG, though. You may want to first enter the following to find out if ~changeLocale is among the supported shortcuts:
Code:
;debugOn
~help
;debugOff
All of these commands are case sensitive and need to entered in the search bar and confirmed by pressing the Enter key. You'll also need to restart the Kindle.