Holmes' trial had been set to begin in February.
Holmes pleaded not guilty by reason of insanity to charges of killing 12 people and injuring 70 at an Aurora theater in July 2012. Prosecutors are seeking the death penalty, and they want Holmes to undergo further evaluation of his sanity.
District Judge Carlos Samour Jr. scheduled hearings on further testing and other pre-trial issues for Dec. 17 and 18.
The findings of Holmes' first mental health evaluation, conducted at a state hospital, have not been publicly disclosed. But the fact that prosecutors want further evaluation suggests that the first exam might have found Holmes was insane.
Holmes' attorneys don't dispute that he committed the shootings, but his plea makes psychiatric evaluations - which assess whether Holmes was sane at the time of the shootings - the most important pieces of evidence.
If doctors who evaluated Holmes concluded he was insane, it would be much harder for prosecutors to persuade a jury to convict him of murder and sentence him to death.
If jurors agreed Holmes was insane, he would be committed indefinitely to the state hospital. He could one day be released If doctors there ever concluded Holmes' sanity had been restored, he could one day be released, but that is considered unlikely.
Colorado law defines insanity as the inability to tell right from wrong because of a mental disease or defect. An evaluation by the state mental hospital is mandatory for anyone who pleads insanity. Holmes underwent his last summer.