How to change the time format display to 24h

Currently all displays of time are in am/pm format like e.g. "Apr 21, 2016 2:49pm GMT+0200" and I would like to have this in 24h time format. Unable to find any documentation on this I tracked this specific configuration down to the file https://gitlab.com/gitlab-org/gitlab-ce/blob/master/config/initializers/date_time_formats.rb and the setting:

Time::DATE_FORMATS[:medium] = '%b %-d, %Y %-I:%M%P'

But now I have no idea how to set this from the outside without modifying the code directly. Is there a way to put this in the gitlab.rb config or another way to overwrite this value?