The longest song ever written and performed began in 1999 and is scheduled to complete the last moment of 2999, one thousand years. Here is a link that talks about the project:
John Cage also produced some experimental concepts. 4’33 is a composition that is simply four and a half minutes of silence. Another composition, ASLSP (As Slow As Possible) began playing in the Burchardi church in Halberstadt, Germany, in 2001 and is to be completed in 2640. It averages about one note change every 7 years.