[Cletus.D.Yokel]

Meaning that the device used has a time stamp set to GMT. Either the user is posting from a location in the GMT area (London) or is using GMT so that their general location cannot be determined.

Each “time zone” is approximately 1000 miles across (E->W) at the equator and ~12,000 miles long. Applying known percentages, only about 1/3 of each time zone is land.

YMMV, depending on latitiude

[Jack Black]

GMT = Greenwich Mean Time, is the time zone that has the 0* N-S meridian running through the middle of it.

The Difference Between GMT and UTC

A lot of places (like computer networks) use UTC now in place of GMT.