The team was due to deposit its findings on the case next week, as part of a review granted earlier this year by an appeal court judge, following defence claims that evidence had been poorly handled and collated.
But Professor Carla Vecchiotti and her colleague Stefano Conti wanted additional time to examine other documents which were drawn up by the original investigators as part of their fresh probe, and this was agreed.
In March leaked details of their initial findings appeared to give fresh hope to Knox - jailed for the murder of student Meredith Kercher in Italy - after the new experts said the evidence was "insufficient to convict her".
Knox, 23, is serving 26 years for the brutal sex killing of Miss Kercher, 21, who was found with her throat in her bedroom in the house they shared. Key to her conviction was a 30cm kitchen knife which contained her DNA on the handle and genetic material - but not blood - from Miss Kercher was found on the blade.
Earlier this year an appeal court judge in Perugia, where the murder took place, authorised an independent review by the two forensic experts from La Sapienza University in Rome. They were also asked to re-examine a bloodied bra clasp belonging to Miss Kercher on which DNA from Knox's co-accused Raffaele Sollecito, 25, was also found - but after it had been "lost" for six weeks.
Computer studies graduate Sollecito, 25, was given 25 years jail and both he and Knox deny any involvement in the murder and are appealing against their conviction.
In the leaked initial findings both said the knife, which was found in Sollecito's kitchen, revealed that the DNA material on it was so slight that it was insufficient to conclusively convict Knox. The amount of DNA was so small that the two professors also concluded it was not enough to carry out a second test on the knife.
While the bra clasp was described as "so deteriorated" that it was impossible to re-examine it for any traces of DNA - it was originally found at the scene but then lost for six weeks before being discovered elsewhere in Miss Kercher's bedroom.
According to the report the clasp - which had been cut from the bra - had been poorly kept in a "liquid jar" and not properly dried which meant that it had "rotted and rusted".
Knox's lawyer Carlo Dalla Vedova said: "We expected them to ask for more time - it's a prerogative of theirs and these experts always do because they want to be sure of their findings.
"The leaked details from earlier this year simply confirmed what we already knew and what we have already said in court - the evidence was insufficient.
"We heard how the clasp had rusted away because it had been kept in a bag of water and the DNA on the knife was too low. We know have to wait for the final report."
The next hearing is due to take place on May 21 when the court will hear from the murder squad chief, Monica Napoleoni, before adjourning until the end of June - meaning a verdict may not come until the autumn.
Miss Kercher, of Coulsdon, Surrey, was in Italy as part of her European Studies degree at Leeds University and had only been in Perugia for two months when she was murdered in November 2007.