Comment 7 for bug 48128

It seems to me that there are two issues here:
1. There is no GNOME-wide way of changing the values of LC_TIME (the bug I linked and referenced by Leo Howell)
2. The default LC_TIME settings for en_GB suck (contentious)

Lets continue to use this bug for 1., if you'd like the default settings for 2. to change please open a bug and report it to the upstream developers (glibc developers?)

As a work around you can add "export LC_TIME=en_DK.UTF8" in your .bashrc file, this will give you 24 hour clock time everywhere that respects the LC_TIME locale.