40 years
The number of changes involved in the complete 12 bell peal is 479,001,600. It is not recorded as having been performed. Usually the maximum rung is a peal of seven bells, the number of possible permutations for which is 5,040 and takes around 2 and half to 3 hours. The peal rung in Dorothy Sayers's acclaimed detective book "The Nine Tailors" was of nine bells and took a marathon 9 hours.