There is a default value called the Inter Digit Timer on a J139 desk phone. This timer controls the amount of time you can pause while entering a number on the phone before the phone dials the number you've entered. I don't know if it also exists on other phones, but I would guess that it does.
The value of the inter digit timer is 3 seconds and apparently cannot be changed. That means that when you're dialing a number on a J139, if you pause for 3 seconds the phone will dial your partially-entered number and you'll get an unhappy message... something like "I'm sorry, you entered an incorrect extension"
There is apparently no way to adjust this from 3 seconds to something more reasonable (like 5 seconds or 7 seconds).
This link (https://onecare.avaya.com/AvayaCloudOffice/kb/public/ADMN116117&viewlocale=en_US) tells how to set the dialing mode to Manual. After setting the dialing mode to Manual you must dial a number and then press Call.
I would like to have the option of extending/changing the inter digit timer.