In order to convert 3 p.m. GMT to a specific time zone, first determine the difference between the local time zone and GMT. After you figure this out, add or subtract that time difference from GMT.
The time observed at the Royal Observatory in Greenwich, London is known as the Greenwich Mean Time (GMT). It has been accepted as a global time standard, and most countries and cities of the world express their local time in relation to GMT. For example, Moscow is at GMT+4 time zone and Boston is at GMT-4 time zone. Therefore, when it's 3 p.m. in GMT, it is 7 p.m. in Moscow and 11 a.m. in Boston.