This time is corrected for local time zones and where possible for daylight saving times.
Each country set the time that they should be referenced to. If we were to use local solar time, then places in the same country or region would have varying times. This could make for some interesting appointment calendars and give some unique excuses for why you slept in. You might make a call to someone at 10 am only to find that the colleague in a nearby town has missed your call because it is 10:15 am there. Doesn’t this make you glad that someone decided that we would set our times zones relative to the Greenwich Meridian and hence the name Greenwich Mean Time (GMT)?
All time zones were set as plus or minus a number of hours from this datum depending on how far east or west they are from the datum with a few local adjustments to keep regions on the whole in the same time zone.
The further East you are, the greater the number of hours ahead of GMT you are. This is because the sun rises earlier in the East relative to GMT and later the further West one is. In more recent times GMT has become synonymous with UTC Coordinated Universal Time.
UTC is now the time coordinated by the scientific community. In some places you may find the time zone for GMT. UTC referred to a “Z” or Zulu in the phonetic alphabet.
For a very interesting trip we would recommend visiting the Royal Museums Greenwich where you can find out more of the history of time measurements.