In 2002, during the 56-year-old's first trial, pathologist James Pang told the court that based on the stomach contents, he estimated the times of death to be roughly an hour after the pair ate dinner -- about 7pm.
Today he said he had changed his position to say Mrs Lundy and Amber could have died anytime within a 14 hour period.
The only certainty about the time of death was that it could have happened anytime between about 7pm on August 29, when they were in contact with someone, until their bodies were found the following day about 9am, he said.
He also defended not taking the temperature of the victims because he did not want to disturb evidence.
Forensic pathologist Martin Sage told the court that whodunnit television programmes and books would often have a pathologist who would easily be able to pinpoint a time of death.
"That is a complete fiction."
In the "real world", timings could not be precise because there could be all sorts of variables, Dr Sage said.
It was known that Mrs Lundy and Amber bought a McDonald's meal at 5.45pm on August 29, and Dr Sage said it was reasonable to assume the meal was eaten a short time later.
However, he said it was not known if they ate something else later that evening, which would affect the time of death estimation.
The court was also told of the injuries suffered by the victims.
Amber was found lying in the hallway in the bedroom doorway to her mother's room in a pool of her own blood with significant head wounds.
Dr Pang said the weapon used on Amber and her mother had "sharp, clean cut edges" and was consistent with a moderately heavy object with a sharp edge and a handle.
Mrs Lundy was found with defensive wounds to her arms and hands, which came from her fighting off her attacker, as well as numerous cuts to her face and head.
Bruising on Mrs Lundy's arms could have come from being hit with the handle of the weapon as she was attempting to defend herself, Dr Pang said.
Throughout the graphic evidence, Lundy sat quietly, occasionally taking notes.
The trial before Justice Simon France continues.