Arrington who has said his client acted in self-defense said Tuesday that he needs more time to secure an expert on bruising and notify prosecutors of the selection.
"Under the rules of evidence, there's no surprise witnesses anymore," Arrington said. "If we come up with a new piece of evidence, we are supposed to give prosecutors 30 days in which to review that and respond."
Arrington said the five-day trial was rescheduled to begin on Sept. 29. Sander will be back in court on April 15 for a status conference.
Dunn's family wrote a letter to 2nd District Judge David Connors expressing their displeasure with another delay pushing back trial in the two-year-old case.
"We are very frustrated and disheartened by the defense attorney's tactics to delay and prolong the trial process," the letter reads. "We are ready for closure."
Dunn died on a bed in the living room of his Bountiful apartment on Feb. 21, 2012, after Sander allegedly stabbed him once in the chest.
The stabbing culminated a day-long drinking binge, Bountiful police Detective Keith Beal testified at Sander's 2012 preliminary hearing. Beal said Sander told him in an interview after the stabbing that Dunn had begun drinking at 9:30 a.m.
By about 11 p.m., Sander had consumed three cans of beer and about five to six inches of a bottle of whiskey, Beal said.
Sander told Beal that she stabbed Dunn after he tried to grope her and kiss her throughout the day. Though the two had dated in the past, Beal said, Sander told him that their friendship during the last six years had been nonsexual, and his advances were not welcomed.
"She said Mike kept doing it, and she stabbed him," Beal said. "She just lost it and stabbed him."
A medical examiner testified at the preliminary hearing that Dunn's blood-alcohol level at the time of his death was 0.23, which is nearly three times the legal limit for driving.
Arrington argued at the preliminary hearing that Sander was defending herself when she stabbed Dunn. He said that if Dunn had survived, he likely would have been investigated for sexual assault charges.