How does GMT work?

You have to do a conversion to your local time.

If you live in the GMT + 5 (Eastern standard time) and wish to find out when an even in GMT + 1 is at you would add four hours. It is the difference between the time zones.

If you want to find out what time an event is at that is GMT - 4 you would add 9 hours, because 5 - -4 is 5+4 = 9.

That is the general rule, your GMT - Other TimeZone.

GMT + 5 - GMT - 4 = 5 - -4

GMT + 5 - GMT + 1 = 5 - 1

Then the result is added to the time.