From the action-bar select File and select Preferences.
In the Preferences window, select Expert Features(1) and check the Enable overburn disc-at-once(2).
Choose a Maximum CD Length(3) and click OK(4) (*82:59:59 is the maximum value I suggest, but as you can see from the screen capture above I have set mine significantly higher. The reason is because I frequently use 99min 850 MB CD media).
For a more accurate test you can use a Nero tool called Nero speed test to see how much a specific CD is capable of being overburned . get it here
From the action-bar select File and select Write CD.
A window will appear when you have exceeded expected length, click OK to start the overburn copy.
Remember to set disk to burn Disc at Once, you cannot overburn in Track at Once Mode.