The sign to the right informs travelers that the station operates on Earth Mean Time
Earth Standard Time, rarely Earth Mean Time, refers to the Earth Alliance's standard solar time.[1]
Since Earthgov is based out of Earthdome in Geneva, Switzerland, EST is essentially the local timezone for Central Europe (CET or UTC+1, CDT or UTC+2 if daylight saving time is used).[2] While the rest of the planet still operates on local timezones, EST is used as a central point of reference by global and interplanetary news services such as ISN and all off-world military outposts, ships and installations.[3]
JMS has also said that Earth Standard Time is UTC, though it is unclear why that would be more practical than synchronizing with the local time zone of the parent government.[4][5]