The GMT hand only moves when the minutes hand is moved, so to move the GMT hand around one whole rotation, you need to spin the minutes hand around the entire dial 24 times, they're designed such that once its set you don't have to worry about it. The 24H hand is actually driven off the minutes hand, and while it doesn't look like the GMT hand moves much, that's because of how low its geared, just keep turning the minutes hand around and around the dial and you'll see the GMT hand move.
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