There are numerous time systems in use in astronomy. For our purposes we will base our predictions on Coordinated Universal Time (UTC) which is much the same as Greenwich Mean Time (GMT ). The GMT abbreviation is used throughout the program.
You can elect to have your time displayed primarily in either system. The time system is toggled by the 'Local/ GMT" button on the main screen next to the time display.
Note that changing between local and real time also affects the date if the time zone subtracts or adds sufficient hours to push beyond a date boundary.