Simon Mann, the British leader of a group of alleged mercenaries, has asked the Zimbabwe High Court to stop his extradition to Equatorial Guinea.
Mann (second right) was due for release in May
Mann's lawyers said he would not have a fair trial in Equatorial Guinea and would face torture there.
He was arrested in 2004 when his plane landed in Zimbabwe. He was accused of trying to fetch arms for a coup in Equatorial Guinea, and jailed.
The High Court hearing on Thursday ended without a ruling.
Mann, a former SAS officer, was due for early release in May for good behaviour.
Also in May, a Zimbabwean magistrate's court agreed to a request by Equatorial Guinea that Mann be extradited to stand trial there.
This prompted Mann's appeal to the High Court. He is to remain in custody until the court rules on his appeal.
More than 60 men arrested with him - most of them South African citizens of Angolan origin - were released in 2005 after serving a year's sentence in Zimbabwe.
Sir Mark Thatcher, son of former UK Prime Minister now Baroness Thatcher, was fined and received a suspended sentence in South Africa for his involvement in the affair.
The relatives of other plot suspects who are being held in Equatorial Guinea have complained of abuse and unfair treatment.
One suspect, a German, died in prison after what Amnesty International said was torture.
Equatorial Guinea, a former Spanish colony, has been ruled by President Teodoro Obiang Nguema since he seized power from his uncle in a coup in 1979.