 Why do the Karna demand the conference begin in three days?
Number two suffered from some sort of emotional block that left him continually on the horns of one dilemma or another. Somewhere out there, the ships of Earth were ranged against the ships of the alien Karna in the most important war that Mankind had yet fought. To have shown himself to one of them would have meant instant loss of prestige. To violate the rigid social setup of Saarkkad would mean the instant closing off of the supply of biochemical products that the Saarkkadic laboratories produced from native plants and animals—products that were vitally necessary to Earth's war, and which could be duplicated nowhere else in the known universe. "A special communication for you has been teletyped in from Earth.
 The Karna are skilled negotiators and want to control the peace talks.
 There is an immediate threat to the planet of Karn, and the Karna desperately need help from Earth.  The Karna are hoping to disrupt Earth's supply chain.  The Karna want to make Earth look bad in the eyes of the other planets.  The Karna are skilled negotiators and want to control the peace talks.