From a very recent update to the EQC FAQ on TC3 land (the text in blue is the recent addition):
How long will EQC take to complete geotechnical engineering work on TC3 properties?
At this stage, we are expecting the drilling in the eastern suburbs to be finished in the next six to nine months. Further announcements around timeframes for the remaining western and southern suburbs will be made when we have a clearer picture of the resources available.
At this stage, it’s difficult to be precise, since details such as the number of drilling rigs and operators, and even the final number of TC3 properties, is still to be determined. Work will start in mid-March 2012 and we anticipate it will take 12-18 months for drilling of worst hit homes to be complete.