I know this sounds crazy, but I've just spent an hour testing it using Chrome and Firefox.

1) Try to set the a date restriction on ANY resource to March 8, 2014, 18:00, save it then check it. It will change to 17:00.
2) Change it to any other day, month, year or hour and it will save correctly.
3) Change it back to March 8, 2014 and set the date to 18:xx (using any minutes you want) and everything will save, but the hour will change from 18 to 17.

I've tested in our production (Moodle 2.5.4+ Build: 20140220), our test environment AND our previous installation (Moodle 2.2.4+ Build: 20120719). All with the exact same results.

Am I going crazy?