Judge Carlos T. Samour Jr. had previously given the Colorado Mental Health Institute at Pueblo until the end of July, but the psychiatrist who will interview Holmes wants to review the 40,000 pages of evidence in the case.
"I don't think I have a whole lot of choice," Samour said of the extension.
Despite the delay Holmes is still scheduled to go on trial in February. The trial can't begin until the sanity evaluation is completed and weeks of motions hearings are held.
Holmes pleaded not guilty by reason of insanity to killing 12 people and injuring 70 others during a midnight showing at an Aurora movie theater on July 20.
He had a tidier appearance in court on Tuesday. His formerly bushy beard was down to a slight shadow on his chin and his hair appeared combed. He smiled when a member of his defense team spoke in his ear.
A handful of shooting victims attended the brief hearing, including Josh Nowlan, who was shot in the leg and arm.
His presence was intended to send a message to Holmes.
"You don't scare me and I will move past this and what you've done to me will never be forgotten but you will never beat me," said Nowlan, a scar still visible beneath is right elbow.
Also during Tuesday's hearing, both prosecutors and defense attorneys objected to turning over the notebook Holmes sent to a psychiatrist to attorneys for Fox News reporter Jana Winter.
Winter is fighting demands from defense attorneys to reveal the source of her report that the notebook included violent drawings. Holmes' lawyers contend that whoever told her that violated a gag order.
Last week, Winter's lawyers said in court documents that they should be allowed to inspect the notebook so they can argue about how significant its contents might be at trial. Prosecutor Rich Orman told Samour turning it over to her lawyers would effectively be turning the evidence over to the media.
Associated Press Writer P. Solomon Banda contributed to this report.