Greenwich Mean Time (GMT) also known as Coordinated Universal Time (UTC) is used worldwide as the official time reference. Time zones are expressed like UTC -3h or GMT -3h, where the "-3h" refers to that time zone being three hours before UTC or GMT. On the other hand, UTC +3h or GMT +3h would refer to that time zone being three hours after UTC of GMT. The difference in time between a Forex broker local time and GMT (UTC) is called Broker GMT offset.
Every Forex broker company has its own GMT offset, while many Forex robots like Volatility Factor EA are GMT dependent, they need to get GMT offset to be set correctly to trade properly and show good results.
Some trading strategies in other Forex robots like Forex Diamond don't require GMT offset to be set in the robot's settings for live trading, instead this might be needed just for backtesting!
In Forex robot strategies using News Filter as in Happy Market Hours, Happy News and Forex Combo System, setting the correct GMT offset is so important otherwise the robot will be unable to detect the right time for the news and events occurrence.
Tickmill MT4 server time will be changed to GMT+2 according to New York DST on the 4th of November 2018, so set your Forex robots correctly!