The extension was granted following the provision by Gunns of additional information which seeks to enhance the environmental position of the mill.
These more stringent environmental aspects have been proposed by the company following consultation with community and environmental non-government organisations.
Gunns has asked Environment Minister Tony Burke to give these improvements regulatory force through the permitting process.
Gunns Managing Director Greg L'Estrange said the enhancements were part of the company's continuing commitment to best practice.
"We want to ensure we build this pulp mill using the best-available technology, with the best environmental controls available," he said.
"We are pleased that Minister Burke and his department are willing to give further consideration to these enhancements."
The deadline for approval has been extended to 10 March 2011.