When it comes to time zones, 9/8c refers to a period when the Eastern time zone is 9 a.m. and the Central time zone is 8 a.m. in the United States and Canada. Those events occur at the same moment, yet the clock displays different times in various longitudes.
The Eastern and Central time zones are four and five hours behind Greenwich Mean Time, respectively. GMT (Greenwich Mean Time) is a universal time system. During the British winter, it is the time at the Royal Observatory in Greenwich, London. It is 9 a.m. Eastern, 8 a.m. Central, and 1 p.m. GMT when it is 9 a.m. Eastern.