It is easy for the #gtchat members who are on American EST to remember the time for the two weekly sessions. For them it is always 12.00 noon and 7.00pm on Friday.
For the #gtchat members from other places such as UK, Ireland, India and Australia the time needs to be determined by using a time zone calculator such as Time and Date World Clock Meeting Calendar http://www.timeanddate.com/worldclock/meeting.html
There is a further complication and that is that the US has just gone on to Daylight Savings time. Some Australian states are still on Daylight Savings time but will be reverting to regular time on the first Sunday in April. There is a great Spicy Nodes Webexhibits article on Daylight Savings times at http://www.webexhibits.org/daylightsaving/nodes.html
So, if my calculations are correct, for #gtchat members in the Australian states of Victoria and New South Wales #gtchat will be at 3.00am and 10.00 am Saturday for the next two weeks and will be at 2.00am and 9.00 am Saturday from 8 April through to October.
For full details about how to participate in #gtchat see Deborah Mersino’s Ingeniosus website http://www.ingeniosus.net/gtchat
And for helpful advice about using Tweet Chat to make it easier to participate in #gtchat see the tutorial by Dazzled and Frazzled from Ireland at http://www.dazzledandfrazzled.com/2011/01/introduction-to-twitter-part-3.html