Santosh,
Were you want to go??
For the better part, GT's are a warmer current/summer fish when you get to the southern extremes like Brisbane on the East Coast and Geraldton on the West.
As Stephen said, places like Cairns/Barrier Reef North are 365 days a year since the water is always warm.
Funny thing can happen out in the Coral Sea....too flat & too warm will push the fish off the flats and out into deep (AKA jigging) water.
November to April is the Cyclone Season for Australia, though unless you need to crawl from Tibet, these days even the travelling fisho can fish the guts out of this season with better forecasting....