The request by Knox's lawyers will be made before a court in the central Italian city of Perugia, where Knox, her ex-boyfriend Raffaele Sollecito and African immigrant Rudy Guede were jailed for murdering Knox's housemate Meredith Kercher, a British exchange student in November, 2007.
Knox and Sollecito are jointly appealing against the 25 and 26 year prison sentences handed to them for murdering Kercher, who was found semi-naked with her throat slit. in the cottage she shared with Knox in Perugia.
The two scientists consulted by Knox and Sollecito's lawyers were expected to finish their review of the DNA evidence used to convict the pair by 9 May but say they need the extra 40 days.
Knox and Sollecito claim they are innocent of Kercher's murder and that they were convicted on the basis of faulty forsensic evidence, including disputed traces of DNA found on a knife prosecutors say was used in the murder and on the clasp of Kercher's bra.
If it proves impossible to carry out further analysis of the DNA evidence, the two experts have been tasked with analysing the methods used by Italian police to test the DNA recovered from the crime scene and to see if cross-contamination of this evidence occurred, as the defence claimed.
African immigrant Rudy Guede, who opted for a separate fast-track trial, is serving a 16-year prison sentence for his part in Kercher's killing.
In its explanation of its ruling last December rejecting Guede's appeal against his jail term, Italy's Supreme Court in February said that Kercher was killed by more than one person in a "brutal" and "orgiastic" attack.
Observers say the ruling is bound to affect Knox and Sollecito's claim that Guede was the sole perpetrator of the crime.