Not really....
...
GMT = Greenwich Mean Time (
originally the local mean solar time measured at the Royal Observatory, Greenwich, London, UK but since 1959/1960 I believe this time is generated by a number of synchronised Atomic Clocks around the world including one at Greenwich)
UTC = Coordinated Universal Time (
ITU standard time used and recognised internationally since 1960 - also recognised in some circles as Zulu time for notation reasons)
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Officially GMT = UTC+0 but in essence they are the same thing. I believe that in practice UTC is derived from GMT, rather than the other way round (
GMT was a time standard established in 1884 and UTC was a term adopted in 1928 by astronomers to refer to GMT). See
here on Wikipedia for details.
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In-game I would expect the Human Universe to run off UTC or a derivative there of for historic and cultural reasons.