The British bank is currently vying with a consortium headed by Royal Bank of Scotland to buy the Dutch bank.
In April, Barclays tabled a £79.9 billion offer for ABN Amro, while the consortium, whose offer is conditional on the inclusion of ABN Amro's La Salle unit, offered $95.5 billion.
Under the original timeframe agreed, Barclays would have had to finalise its offer this week.
However, a ruling from stock market regulator AFM means that Barclays will now have until July 23rd to submit its terms in a formal manner.
AFM granted the extension on the grounds that regulatory scrutiny of the bid is ongoing.
A statement from Barclays said: "Since the regulatory review processes relating to the documentation are not yet completed, the AFM has agreed an extension so that an announcement on the availability of the formal offer documentation can take place on or before July 23."
It added: "Good progress continues to be made in relation to the pre-conditions, documentation and regulatory change of control approvals."