Panama City, Fla. is located in the Eastern Standard Time zone. In the United States, the Eastern Standard Time zone is the Greenwich Mean Time, or Universal Time, minus five hours.
There are four time zones in the continental United States. From east to west, they are Eastern, Central, Mountain and Pacific. Each time zone is measured as a variant of the GMT, which is measured from the Greenwich Meridian at England's Greenwich Observatory. Astronomers declared this to be the prime meridian at a conference held in 1884. The entire state of Florida is part of the Eastern time zone, although some states straddle two time zones.