Rev Hassan Abduraheem and Rev Kuwa Shamal face at least seven charges including waging war against the state and espionage, which carry the death penalty as the maximum sentence.
They are on trial with two other mean, Petr Jašek and Abdulmonem Abdumawla.
The hearing, which was due to take place on 31 October in Khartoum, was rescheduled, as the judge was absent. Last week, a hearing scheduled for 24 October was postponed to 31 October, because the judge was out of the country.
Christian Solidarity Worldwide, which is monitoring the case, told Premier it was concerned the delays would mean the men would not get a fair trial.
There has already been several other delays to the case, including a three-week adjournment for the translation of documents.
The case against the pastors centres on money given to a young man who was injured in a protest against the state.
CSW's Chief Executive Mervyn Thomas said: "We are concerned by the continuing delays in the trial.
"Fair trial principles stipulate that criminal proceedings should occur within a reasonable time. In this case, the constant postponements due to the absence of the judge or prosecutor or failure to transport the men to court are prolonging proceedings unnecessarily, which is unacceptable, given the length of time these men have already spent in custody.
"We continue to call for the unconditional and immediate release of these unjustly detained men. In the event the trial continues, we urge the government of Sudan to ensure it proceeds in line with fair trial principles outlined in Article 7 of the African Charter on Human and Peoples Rights, to which Sudan is a party."
