Aaron Schaffhausen, 35, of Wisconsin, is charged with three counts of first-degree intentional homicide and one count of attempted arson after his daughters were brutally murdered on July 10. Those killed included Amara, 11, Sophie, 8, and Cecilia, 5.
In January, he pleaded not guilty by reason of mental disease or defect, but he is expected to change his plea and admit he killed his daughters by slitting their throats.
"We will know tomorrow," Judge Howard Cameron said.
Defense attorney John Kucinski said, "I think we're going to change our plea; change it to guilty by reason of mental disease or defect."
Trial is set to begin on Monday.
Kucinski had no reason for his client's decision, saying that it was "subject to people changing their minds in the morning."
If he does change his plea, the trial will shorten, as it was first scheduled to last up to three weeks.
He could face life in prison if he is found guilty and sane, but if he is found guilty and insane, he would be committed to a mental health institution until a court believes he will no longer be a danger to himself or others.
The father is accused of killing his girls after he surprised his ex-wife Jessica with a visit. He convinced her to let him baby sit. After she left, he called her a few hours later and said, "You can [come] home now because I killed the kids."
When authorities arrived, they found the three girls each tucked in their own bed with blood on their faces and necks.
An autopsy declares their cause of death as "sharp force injury to the neck." One child, Cecilia, was also strangled.
The couple divorced last January. He was living in North Dakota while the girls and the mother lived in Wisconsin.
Though the man previously threatened the mother's life, she said he could babysit the kids as they were eager to see him.
The girls were being babysat by a woman when the father arrived. The babysitter said the girls were excited to see him when he came. As she left, they took him upstairs to show him their toys.
Two hours later he called his ex-wife and told her he killed them.
After the police arrived and saw the girls, they also discovered that he had poured a container of gasoline in the basement, indicating he may have been planning to set the house on fire.
He turned himself into police about an hour after he contacted the mother. He did not say anything when detectives tried to interview him.